Biofluid Activated Microbattery for Disposable Microsystems

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Title:
Biofluid Activated Microbattery for Disposable Microsystems
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1 online resource (50 p.)
Language:
english
Creator:
Garay, Edgar F
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University of Florida
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Gainesville, Fla.
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Thesis/Dissertation Information

Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Electrical and Computer Engineering
Committee Chair:
BASHIRULLAH,RIZWAN
Committee Co-Chair:
NISHIDA,TOSHIKAZU
Committee Members:
BOSMAN,GIJSBERTUS

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Subjects / Keywords:
battery -- biofluid -- biomedical -- disposable -- mems -- microbattery -- microelectromechanical
Electrical and Computer Engineering -- Dissertations, Academic -- UF
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Electrical and Computer Engineering thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

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Abstract:
A flexible microbattery activated by blood, urine, saliva, or aqueous sodium hydroxide for disposable medical and biological microsystems is presented.  We developed a new CMOS compatible process in order to fabricate a microbattery on a flexible polyimide substrate using conventional MEMS techniques. The microbattery has interdigitated electrode geometry and uses aluminum as the anode, silver oxide as the cathode, and copper as the current collectors. Two different silver oxidation methods were explored to optimize battery performance. The proposed microbattery has a minimum footprint area of 12 mm2 and is activated by micropipetting 8 µL of the activation fluid onto the surface of the battery. Seven different batteries having different electrode width and spacing were fabricated and characterized. The experimental results show a maximum voltage output of 1.75 V, current output of 0.55 mA, capacity of 7.17 µAh, and a maximum operating time of 75 minutes.
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In the series University of Florida Digital Collections.
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Includes vita.
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Includes bibliographical references.
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Description based on online resource; title from PDF title page.
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This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility:
by Edgar F Garay.
Thesis:
Thesis (M.S.)--University of Florida, 2013.
Local:
Adviser: BASHIRULLAH,RIZWAN.
Local:
Co-adviser: NISHIDA,TOSHIKAZU.
Electronic Access:
RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2014-06-30

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Applicable rights reserved.
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lcc - LD1780 2013
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UFE0046401:00001


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BIOFLUID ACTIVATED MICROBATTERY FOR DISPOSABLE MICROSYSTEMS By EDGAR FELIPE GARAY A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013

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2013 Edgar Felipe Garay

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To my mother, for all her love and support

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4 ACKNOWLEDGMENTS I would like to thank my mother, Irene family, professors, and friends who have provided me with the emotional support and valuable advice that has helped me during I am grateful for the example my mother ha s always set for me by working hard every day I also want to thank Irene for his love and support. In addition, I want to express my gratitude towards my mentor, Dr. Rizwan Bas hirullah, for nurturing my enthusiasm for science.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 6 LIST OF FIGURES ................................ ................................ ................................ .......... 7 LIST OF ABBREVIATIONS ................................ ................................ ............................. 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 MOTIVATION ................................ ................................ ................................ ......... 10 2 BATTERY THEORY ................................ ................................ ............................... 12 Battery Performance Metrics: ................................ ................................ ................. 13 Batteries at the Microscale ................................ ................................ ...................... 15 On Demand Microbatteries ................................ ................................ .............. 15 Additional Microbattery Systems ................................ ................................ ...... 18 3 SILVER OXIDE ALUMINUM BATTERY ................................ ................................ 22 Usage Model ................................ ................................ ................................ ........... 22 Al AgO Battery Chemistry ................................ ................................ ....................... 23 Battery Design and Fabrication ................................ ................................ ............... 24 Fabrication Process Flow ................................ ................................ ........................ 25 Cathode and Anode Fabrication ................................ ................................ ....... 28 Microbattery Release ................................ ................................ ....................... 30 4 RESULTS AND DISCUSSION ................................ ................................ ............... 33 Microbattery Structure and Composition ................................ ................................ 33 Electrical Characterization ................................ ................................ ...................... 33 Sodium Hydroxide Electrolyte ................................ ................................ .......... 35 Microbattery Activated by Biofluids ................................ ................................ ... 40 Conclusions ................................ ................................ ................................ ............ 45 LIST OF REFERENCES ................................ ................................ ............................... 47 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 50

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6 LIST OF TABLES Table page 2 1 Electrochemical equivalents of common anode and cathode mate rials ............. 16 3 1 Microbattery sizes with the ir respective naming convention ............................... 26 3 2 Different methods for depositing Silver Oxide and thei r measured open circuit voltage ................................ ................................ ................................ ................ 29 4 1 Electrical performance comparison for microbatteries activated using NaOH. ... 39 4 2 Electrical performance of microbatteries a s a function of area and volume ........ 39 4 3 Capacity of microbatteries activ ated using physiological fluids .......................... 40 4 4 Electrical performance of microbatteries activated using physiological fluids as a function of area and volume. ................................ ................................ ....... 40 4 5 Performance comparison between our microbatteries and prev iously published microbatteries ................................ ................................ ..................... 44

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7 LIST OF FIGURES Figure page 2 1 Battery schematic and operation ................................ ................................ ........ 12 2 2 Ragone plot sh owing electrical performance of conventional battery technologies and the best previously published microbatteries. This plot was adapted from Pikul et al. [28] ................................ ................................ .............. 20 3 1 Micro battery usage model where the analyte is used to activate the battery ...... 23 3 2 Flexible microbattery electrode geometry and cross sect ional views of the microbattery ................................ ................................ ................................ ........ 25 3 3 Fabrication process of the microbattery. ................................ ............................. 27 3 4 Two different metho ds used to deposit silver o xide ................................ ............ 29 3 5 Microbattery dicing and release by plasma etching Si substrate ........................ 31 3 6 Microbattery images. ................................ ................................ ......................... 31 3 7 Microbattery electrodes on a polyimide substrate attached to a gelatin capsule. Photo courtesy of Edgar Garay. ................................ ........................... 32 4 1 XEDS spectrum and SEM mi crograph s. ................................ ............................. 34 4 2 Experimental output voltage for microbatteries ................................ ................... 36 4 3 Microba ttery experimental efficiency. ................................ ................................ 37 4 4 Voltage output for microbatteries activated using different electrolytes .............. 41 4 5 Voltage output for microbattery type S60 and S45 activated using blood ........... 42 4 6 Ragone plot comparing the performance of our microbattery with previously published batter ies and commercial technologies ................................ .............. 43

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8 LIST OF ABBREVIATIONS Al Aluminum AgO Silver Oxide CMOS Complementary metal oxide semiconductor Cu Copper IC Integrated circuit l Electrode length LOC Lab on a chip MEMS Microelectromechanical systems OH Hydroxide PI Polyimide PR Photoresist RF Radio frequency s Electrode spacing Si Silicon SiN Silicon Nitride Ti Titanium w Electrode width

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9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science BIOFLUID ACTIVATED MICROBATTERY FOR DISPOSABLE MICROSYSTEMS By Edgar Felipe Garay December 2013 Chair: Rizwan Bashirullah Major: Electrical and Computer E ngineering A flexible microbattery activated by blood, urine, saliva, or aqueous sodium hydroxide for disposable medical and biological microsystems is presented. We developed a new CMOS compatible process in order to fabricate a microbattery on a flexible polyimide substrate using conven tional MEMS techniques. The microbattery has interdigitated electrode geometry and uses aluminum as the anode, silver oxide as the cathode, and copper as the current collectors. Four different silver oxidation methods were explored to optimize battery perf ormance. The proposed microbattery has a minimum footprint area of 12 mm 2 and is activated by micro pipetting 8 L of the activation fluid onto the surface of the battery. Seven different batteries having different electrode width and spacing were fabricate d and characterized. The experimental results show a maximum voltage output of 1.75 V, current output of 0.55 mA, capacity of 7 .1 7 Ah, a nd a maximum operating time of 7 5 minutes.

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10 CHAPTER1 MOTIVATION The continued trend towards CMOS scaling has allowed integrated circuit (IC) designers to implement complex ultra low power systems that can be turned on using only a fraction of a volt [1 4] The recognition that such low power systems are capable of gathering, analyzing, and transmitting data has fueled the search for new disposable devices, such as electronic RFID tagging devices for medication compliance, lab on a chip (LOC) for health screening, and food sensors, among others [5 8] As a result, batteries at the micro scale are becoming more adequate as power sources for these devices. Unfortunately, battery manufacturers still employ manufacturing techniques that are not capable of de livering disposable and biocompatible power sources with a small enough form factor that could be integrated with the before mentioned microsystems. Many of the research efforts have been directed towards the utilization of semiconductor device fabrication technology to develop batteries at the micro scale [9 13] A variety of microbattery architectures have been proposed ranging from complex 3 dimensio nal structures to ink jet printed batteries [14 17] but many obstacles are still impeding their imp lementation into microsystems. The proposed microbatteries employ intricate microfabrication schemes that involve the injection and encapsulation of the electrolyte, which hinders the possibility of mass producing them at a low cost [11, 18] In addition to the small energy content, batteries using corrosive electrolyte suffer from a high self discharge rate that translates into a short battery shelf life. For batteries using solid electr olyte, the high temperature steps in the manufacturing process renders the fabrication incompatible with conventional IC fabrication [19, 20] Disposable microbatteries that have been proposed in the past employ a difficult stacking of

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11 multiple layers in order to separate the electrodes to make room for the electrolyte to flow [21] Biofluid acti vated batteries using water and urine as the activation fluid and having a footprint area of 24 cm 2 have also been demonstrated in the past [22 25] The large footprint area of the battery and the plastic lamination technology used for fabrication do not make it a viable solution as a power source for medical and biological microsystems. There is a current need for a low cost, flexible, on demand, and biocompatible battery that could be easily integrated with low power medical and biological microsystems. This work presents a concept for a disposable, flexible and conformal paper like microbattery to enable new modes of use of inexpensive biosensors in point of care settings.

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12 CHAPTER 2 BATTERY THEORY A battery is a system composed of one or more electrochemical cells that convert the chemical energy stored in its active components into electric energy. These types of cells are known as galvanic cells and perform energy conversion through an electrochemical oxidation reduction process, also known as a redox reaction. In the case of a rechargeable cell, this reaction occurs in two directions for ch arging and discharging. There are three major components in a cell: anode or negative electrode, cathode or positive electrode, and electrolyte. When the anode and cathode are connected through an external load, the anode is spontaneously oxidized in the presence of the electrolyte and gives up electrons to the external circuit. The anode accepts these electrons from the external circuit as it is being reduced. The electrolyte is responsible for providing the conductive medium for the ionic charge transfer between positive and negative electrode. The schematics of a convention al battery are shown in Figure 2 1. Figure 2 1. Battery schematic and operation.

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13 Batteries are classified according to their electrical capabilities as primary and secondary batteries. Additionally, batteries are also classified depending on their usage model and design. In primary batteries, the electrochemical reaction is not reversi ble or cannot be effectively reversed, therefore once fully discharge they have to be thrown away. Primary cells are often used in a variety of consumer electronic products where a long shelf life and high energy density at low discharge rates are needed. On the other hand, rechargeable or secondary batteries can be restored to their original condition by supplying a current through their terminals in the opposite direction of the discharge current. The energy density and capacity retention is usually lower than in primary batteries, but their ability to be charge and discharge at high current rates make them ideal for portable electronics. Within primary batteries, reserve batteries are a type of unrechargeable cells in which a main component of the battery is added moments prior to operation. Cells that employ high energy density materials suffer from a high rate of self discharge, which hinders their implementation in real systems. In this type of batteries, liquid electrolyte is the component added prior to operation in order to obtain long storage periods without depleting the stored energy by self discharge. Reserve batteries are used in systems that require extremely high power and long storage periods, such as torpedoes, missiles, and other underwater military applications. Battery Performance Metrics: Experimental battery performance depends on the chemistry of the cell, and varies from the theoretical performance depending on the efficiency. The theoretical voltage (V) of the cell or standard potenti al is calculated form the free energy data under standard conditions. The experimental output voltage of the cell during discharge will depend on the discharge conditions and usually varies depending on the battery state of

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14 charge. Depending on the chemist ry, some batteries will discharge at a constant voltage while others will gradually decrease their output voltage until fully discharged. Overpotentials in a galvanic cell can also lower the maximum experimental voltage obtained. Batteries are also charact erized in terms of capacity. For a battery, capacity is the amount of charges that can be extracted or stored and is commonly reported in amperes hour (Ah) or Coulomb (C). In the case of a resistance static measurement the experimental capacity can be foun d using the following equation: ( 2 1) where i is the current drawn from the battery in A and C exp is the battery capacity in Ah. The amount of energy extracted from the battery is another useful parameter used to c haracterize battery performance. Energy is usually reported as watt hour (Wh) or joules (J) and can be found using the following equation: ( 2 2) where v is the output voltage in V and i is the output current in A. Additionally, the maximum power (W) that the battery can output can be obtained: ( 2 3) where v max and i max are the maximum voltage and current drawn from the battery. From these values efficiency can also be calculated by comparing experimental and theoretical values. It is customary to normalize these qu antities by weight and volume in order to compare performance among batteries. In industry, batteries are characterized by fully discharging the battery in a period of 20 hours at a constant current. The capacity of the battery is then calculated by multip lying 20 hours times the current and is reported in mAh. The discharge current is then label C/20; here C stands for capacity

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15 and not for coulombs. For example, if the battery was discharged at a constant current of 200mA, then the capacity would be 4000mA h for a C/20 rate. It should be pointed out that if the battery is discharge at a rate of 1C, the discharge time most likely would be close to 40 minutes and not 1 hour. This is due to the Peukert effect which lowers the capacity when discharging at higher current densities. For batteries at the microscale is useful to normalize by the footprint area in cm 2 and battery thickness in m. Therefore, units are Ah/cm 2 m for capacity, Wh/cm 2 m for energy density, and mW/cm 2 m for power density. Batteries at the Microscale Over the past decades, low power wireless links have opened the doors for a new array of microsystems that are able to gather and transmit data while consuming an average power of less than 100 W [3] Thes e improvements are the driving force behind the research focused on finding new materials and battery geometries at the microscale that will help create a battery that deliver s enough energy and power to miniaturized wireless nodes. Micro batteries can be c ategorized into thin film, thick film, solid state, printed, three dimensional, and on demand microbatteries. Commercial realization of microbatteries is not possible yet, since device performance is still far from optimal. Additionally, concerns regarding scalability, stability, and fabrication costs still need to be addressed. On Demand Microbatteries Among new microbattery designs, an innovative battery type has emerged that utilizes biofluids as the activation electrolyte for on demand use. These micro batteries employ the same usage model as reserve batteries, in which the

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16 electrolyte is added to the battery moments prior to use. On demand microbatteries can potentially provide enough power and energy for lab on a chip applications, food sensors, medica l implants, and many other biomedical applications. In the case of lab on a chip applications, the microbattery would use the test liquid as the electrolyte to convert the stored chemical energy into electrical energy. Depending on the battery chemistry, p hysiological fluids, such as blood, urine, and saliva could also be used as the electrolyte. One of the main advantages of on demand microbatteries is that highly active materials can be implemented in a small foot print to obtain sufficient energy without suffering from hig h self discharge rates. Table 2 1 shows the theoretical capacity of different materials. As an example, Al and AgO are two of the materials with the highest capacity density, but it is difficult to implement them in real battery systems due to their instability and high self discharge rate. Table 2 1. Electrochemical equivalents of common anode and cathode materials. Material Standard potential (V) Ah/g Ah/cm Anode Material Li 3.01 3.86 2.06 Mg 2.38 2.2 0 3.8 0 Al 1.66 2.98 8.1 0 Ca 2.84 1.34 2.06 Fe 0.44 0.96 7.5 0 Zn 1.25 0.82 5.8 0 Pb 0.13 0.26 2.9 0 (Li)C 6 2.80 0.37 0.84 Cathode Material O 2 1.23 3.35 MnO 2 1.26 0.31 1.54 NiOOH 0.49 0.29 2.16 CuCl 0.14 0.27 0.95 AgO 0.57 0.43 3.2 0 Ag 2 O 0.35 0.23 1.64 Li x CoO 2 2.7 0 0.14

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17 On demand m icrobatteries using sulfuric acid and hydrogen peroxide as the electrolyte have been previously developed [21] This battery employs gold and zinc as the electrodes and silicon as the substrate. The battery was fabricat ed using convention al MEMS techniques for depositing and patterning the gold electrode and the cathode and anode separator. The fabrication is completed by manually bonding a thi ck (~1 mm) piece of zinc on top of the battery. The total area of the battery was 1 mm 2 and exhib its a maximum energy density of 204 Wh cm 2 and a maximum output voltage of 1.5 V The highly corrosive electrolyte prevents the safe integration of this battery into biomedical microsystem. Sammoura et al fabricated a water activated microbattery for BioMEMS chips by using a one mask MEMS process [25] This battery prototype used a 15 m thick magnesium anode and a 20 m thick AgCl cathode. The two electrodes are deposited i nto a silicon substrate and are bonded together using and adhesive, which also serves as a separator. The electrode separation ranged from 50 to 200 m. A battery with a 1.44 cm 2 electrode area exhibited a maximum output voltage of 1.65 V and a maximum e ne rgy capacity of 1.8 mWh. The authors also demonstrated that decreasing the gap between anode and cathode can improve the efficiency of the battery. The first on demand paper battery activated by urine was previously demonstrated by Lee [22] The battery used Cu and Mg electrode s and a CuCl doped filter paper This battery was fabricated using an inexpensive plastic lamination process in which thick (~0.2 mm) sheets of Mg, Cu, Al, filter paper, and plastic film are stacked together to form the battery. The total area of the battery is 18 cm 2 and is able to provi de a maximum power output of 1.5 mW. A second prototype for this battery was

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18 developed where the battery was activated using urine, water, and saliva [23] The battery had an area of 24 cm 2 and it was fab ricated using the same chemistry and lamination technology. The battery exhibited a maximum output voltage of 1.56 V that decreased over time and a maximum power output of 15.6 mW Another example of an on demand and biocompatible battery was proposed b y Jimbo and Miki in which the gastric fluid in the stomach was used as the activation electrolyte [24] This battery consists of a Pt and Zn electrodes on a glass substrate, a porous ceramic filter, and a PDMS case. The fabrication process consisted on sandwiching the ceramic filter in between the electrodes and the using a PDMS to case to hold them together. The battery had a total area of 120 mm 2 and a thickness of 4 resistor. The maximum energy capacity achieved was 0.1 mWh when u load resistor, which translates into an energy density of 0.021 W h cm 2 m 1 Additional Microbattery Systems The first 3 D rechargeable Lithium ion thin film microbattery was developed in 2005 by Nathan et al. [10] This microbattery used a perforated silicon substrate with through holes formed by plasma etching. The fabrication of the battery consisted of different electroplating steps and the preparation and spin coating of a slurry to fill the cylindri cal cavities of the battery. The microbattery had a disc like form factor with a diameter of 13 mm and a thickness of 0.5 mm. The output voltage ranged from 2.2 to 1.2 V maximum and the microbattery displayed a capacity of 2 mA h cm 2 Additional 3 D microb attery architectures have been developed in the past in which silicon micromachining techniques and electroplating are utilized to fabricate them. Chamran et al. developed a Ni Zn rechargeable microbattery using interdigitated electrode arrays

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19 composed of high aspect ratio microscale posts [11] The results indicated that the battery could only be used for a few cycles due to the etching of th e electrodes by the electrolyte. A different approach to 3 D microbatteries was taken by Min et al. in which the used a carbon microelectromechanical systems (C MEMS) microfabrication process to fabricated a Li ion battery [26] The battery consisted of arrays of carbon posts interdigitated with arrays of dodecylbenzenesulfonate doped polypyrrole and a 1 M LiClO 4 electrolyte. The battery prototype demonstrated that it could funct ion as a secondary battery with an areal capacity of 10.6 Ah cm 2 On the other hand, the battery exhibited a short life of only 12 recharging cycles due to an internal short. An all solid state Li ion battery employing a honeycomb pattern was previously developed by Kotobuki et al. [27] The authors studied the properties of the interface between the solid electrodes and solid electrolyte. The output voltage of the battery was 1.2 V and a discharge capacity of 32 Ah cm 2 A different solid state lithium microbattery was developed by Song et al. using a microfabrication process [19] The area of a single microbattery was 500 m x 500 m and its thickness was 1.5 m. The fabrication included a high temperature step of 500 C. The battery delivered a maximum capacity of 17 nAh and could be discharged at a maximum cur rent of 40 nA. The need for smaller batteries with a high energy density has motivated the development of additional methods for fabricating batteries. Ho et al. developed a direct write dispenser printing method to fabricate a Zn and MnO 2 microbattery with an ionic

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20 Figure 2 2. Ragone plot showing electrical performance of conventional battery technologies and the best previously published microbatteries. This plot was adapted from Pikul et al. [28] liquid gel electrolyte. Their first experiments showed that the battery had a capacity of 0.98 mAh cm 2 for more than 70 cycles. A different method for depositing thick film electrodes employs a laser direct write technique [29] In this method, a laser pulse is used to transfer ink or paste onto a substrate. Thick film microbatteries using this method exhibited a capacity of 2500 Ah cm 2 Thick film microbatteries have a higher areal capacity than thin film microbatteries due to the ir large volume. Recently, Pikul et al. developed a high performance 3 D lithium ion microbattery having a power density greater than that of super capacitors [28] The

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21 battery consisted of interdigit ated electrodes in which a porous metallic scaffold was used to electroplate the active materials. The microbattery used a 1 M LiClO 4 liquid electrolyte and a silicone cover to hold the liquid. The total volume of the cell was about 0.3 mm 3 and it showed e nergy densities form 2.5 to 15 Wh cm 2 1 and a maximum power density of 7400 15 W cm 2 1 This is equivalent to 2000 times the power density of the best microbatteries in literature and larger energy density than batteries in previously published wor k The performance comparison of conventional battery technolog ies and best performing published microbatteries is shown in Figure 2 2.

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22 C HAPTER 3 SILVER OXIDE ALUMINUM BATTERY Usage Model We designed the microbattery as a disposable and on site activated battery on a flexible polyimide platform for lab on a chip applications. This microbattery exploits the chemical reactivity of the analyte being tested by using it as an electrolyte in order to convert the stored chem ical energy of the microbattery into electrical energy. This simple approach avoids the need for fabricating a sealed container and injecting the electrolyte. Additionally, the self discharge due to the parasitic corrosion of the electrodes when the electr olyte is present is eliminated. Furthermore, the microbattery can be activated with a range of different biofluids, such as blood, urine, saliva, water, milk, and any other aqueous solution containing the hydroxide ion. Fig ure 3 1 shows the intended usage model for the microbattery. Three different criteria were applied when designing the microbattery: ease of fabrication, CMOS compatibility, and minimization of the battery internal resistance. For the microbattery fabrication, we utilized a CMOS compatibl e MEMS manufacturing technology [30] The simple fabrication steps and lo w temperature process developed for this work, allows for an easy scalability to volume manufacturing and integration with CMOS ICs. Moreover, the ability to implement different designs within the same mask allows for the manufacturing of microbatteries ha ving different capacities, thus permitting the fabrication of microbatteries for different applications within the same wafer.

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23 Figure 3 1. Microbattery usage model wh ere the analyte is used to activate the battery Al AgO Battery Chemistry The microbatteries in this work use aluminum (Al) as the anode and silver oxide (AgO) as the cathode. Large scale batteries based on aluminum silver oxide have found use as power sources in military underwater applications due to their high energy density and prolonged storage periods [31] Al was chosen as the anode due to its electrochemical properties, easy of fabrication and potential use as a biocompatible material. This type of batteries uses an alkaline solution as the electrolyte, making the hydroxide ion the responsible for the c onduction inside the battery. The major chemical reactions for the oxidation at the anode and the reduction at the cathode are given by Equation 3 1 and Equation 3 2 [31 33] : ( 3 1 ) ( 3 2 ) and the overall cell reaction is given by: ( 3 3 )

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24 T he standard potential of this cell is obtained from the free energy data under standard conditions. Depending on the oxidation state of the silver the theoretical open circuit cell voltage ranges from 2.695 to 2.952 V. However, batteries using aluminum as the anode material tend to operate at a lower potential due to the parasitic corrosion of the aluminum and because at room temperature aluminum forms an oxide layer that increases the internal resistance of the battery [34] Battery Design and Fabricat ion The microbattery consists of a series of interdigitated electrodes that alternate between anode and cathode. We chose this battery geometry to minimize the internal resistance of the battery, maximize the surface area, and to avoid complicated fabrication schemes that ultimately will hinder the scalability of the microbatteries to large volume manufacturing. In addition, the interdigitated electrodes allow for the battery to be flexed without delamination of the metal layers due to the stresses caused by the bending of the battery. Current collectors for the an ode and cathode were fabricated from copper (Cu) in order to offset the increase of internal resistance during the operation of the battery due to the low conductivity of the silver oxide and the aluminum depletion. Silicon nitride was used as the insulati ng layer to avoid short circuiting the anode and the cathode current collectors when the liquid electrolyte is present. Seven microbattery designs having different electrode finger widths (w) and electrode spacing (s) were fabricated. The bat teries dimensi ons are shown in F ig ure 3 2 and Table 3 1 summarizes the different microbattery geometries and the naming convention used in this paper for each microbattery. The fabrication of the microbatteries was carried out in a class 100 1000 cleanroom facility. All metals were

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25 Figure 3 2 Flexible microbattery electrode geometry and c ross sectional views of the microbattery. d eposited using a KJL CMS 18 sputtering deposition system. All the UV lithography steps were performed using the EVG 620 mask aligner. F abrication Process Flow The process flow for the fabrication of the microbattery is depicted in Fig ure 3 3 A 100 mm mechanical grade silicon wafer was used as the carrier wafer for the entire fabrication process. The silicon wafer was cleaned by dipping t he wafer in hydrofluoric acid for 30 seconds and then rinsing it in DI water. The first step as shown in Fig ure 3 3 A was to deposit the polyimide. Polyimide was chosen as the flexible platform for the microbatteries due to its biocompatibility and capabili ty of resisting SiN d eposition.VM 652 (HD MicroSystems) was used as the adhesion promoter between the polyimide and the silicon wafer. The VM 652 was dispensed on the static substrate and held for 20 seconds on the wafer. The adhesion promoter was then dri ed by spinning the wafer at

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26 Table 3 1. Microbattery sizes with their respective naming convention. 4000 rpm for 30 seconds. Following the application of the adhesion promoter polyimide was deposited by spin coating PI 2611(HD MicroSystems). Then, the wafer was soft baked at 90C for 120 s followed by 150C for 90 s. Following the soft bake, the polyimid e was fully cured by baking the wafer at 350C in a nitrogen atmosphere for 1 hour. The temperature of the oven was gradually increased at 4C/min from 150 to 350C. After fully curing the polyimide the oven was turned off and the wafer was left overnight inside the oven allowing the wafer to gradually cool down to room t emperature. The final polyimide thickness was roughly 8 m. After the wafer reached room temperature, a 6 m thick positive tone photoresist (PR) (AZ 9260, MicroChemicals) layer was patter ned using conventional UV lithography. In our fabrication process, we designed the PR layer to serve two different purposes. The PR is first used as the mask to etch the polyimide, and then the same PR layer is used after the polyimide etching to pattern t he anode and cathode current collectors. By etching the polyimide and then depositing the collector material using the same mask, the need for planarization steps and a thick SiN layer were avoided. These two steps are described below.

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27 Figure 3 3 Fabricatio n process of the microbattery. A ) spin coat PI, fully cu re PI, spin coat and pattern PR. B ) dry etch PI. C ) Sputter Ti/Cu anode and cathode current collectors and pattern by dissolving PR in acetone D ) Deposit SiN u sing PECVD, spin coat PR etch mask, dry etch SiN E ) Sputter Al anode, pattern using lift off F ) Deposit AgO using reactive sputtering G ) Release microbattery by etching Si using DRIE. The polyimide was dry etch using the Unaxis Shuttlelock reactive ion etcher with an inductively coupled plasma module (RIE/ICP) ( Fig ure 3 3 B ). The process gases for the polyimide etch are O2 and Ar. The etch process follows the recipe developed in [35] Finding the etch rate of the polyimide was crucial in the fabrication of the A B C D E F G

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28 microbatteries. The etch depth had to be the same as the metal thickness of the current collectors so a planar surface could be obtained after the metal deposition. The current collectors were deposited by sputtering a 100 nm thick Ti adhesion layer followed by a 1 m thick Cu layer. The collectors were defined by lifting off the PR in acetone w hile sonicating for 60 s ( Fig ure 3 3 C ). After the lift off process, the metal patterns were inspected using an optical microscope. The optical micrographs indicated poor adhesion between the polyimide and the current collectors. Different approaches were used in order to imp rove the adhesion. Finally, soft baking of the wafer at 112C for 3 min prior to metal deposition greatly improved the adhesion of the metal layers to the polyimide. A 15 min sonication test was used in order to test for proper adhesion. Current collecto r patterning was followed by depositing a 100 nm SiN layer using the STS 310PC PECVD system. The nitride layer provided the necessary insulation for the current collectors. The SiN was patterned using PR as the etch mask and dry etched using the Unaxis RIE /ICP ( Fig ure 3 3 D ). The RF1 power was set to 100 W and the RF2 power was set to 0 W. The process gases were CHF3 and O2 and were set to 27 sccm and 5 sccm, respectively. The chamber pressure was set to 100 mTorr. The SiN etch rate was approximately 125 /m in. Cathode and Anode Fabrication The cathode and anode were sputtered and patterned using conventional lift off techniques. For the anode, a 100 nm Ti layer was sputtered followed by a 1m thick Al layer ( Fig ure 3 3 E ). For the cathode, four different recipes using two different methods for oxidizing Ag were attempted (Figure 3 4) We used the following criteria to select the

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29 Figure 3 4. Two different methods used to deposit silver oxide. Table 3 2. Different methods for depositing Silver Oxide an d their measured open circuit voltage. appropriate method: ease of fabrication and open circuit voltage. The open circuit voltage between Al and AgO was tested using a 1M aqueous solution of NaOH at room temperature. For all four methods, 1 cm silicon squares were cleaved from a silicon wafer to use as the substrate. Then, a 10 nm Ti adhesion layer was sputtered followed by a 200 nm Ag layer. For the first two recipes, the oxidation of the Ag film was accomplished by exposing the silver layer to oxygen plasma using the Unaxis SLR RIE/ICP. For both recipes, the pressure chamber was kept at 10 mTorr, the oxygen flow was set to 40 sccm, and the RF1 power was fixed at 100 W. The RF2 powers for recipe 1 and 2 were 200 W and 1000 W, respectively. The processing time was 5 min. For Sample Oxidation method Open Circuit Voltage (V) Sputtered Ag None 1.71 Recipe 1 Unaxis RIE/ICP plasma, RF2 = 200 W 2.01 Recipe 2 Unaxis RIE/ICP plasma, RF2 = 1000W 2.02 Recipe 3 Reactive sputtering, 5% 1.95 Recipe 4 Reactive sputtering, 10% 1.95

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30 recipes 3 and 4, AgO was directly deposited onto the wafer using reactive sputtering. The percentage of O 2 flow with respect to Ar for recipe 3 and recipe 4 was set to 5% and 10 %. Table 3 2 shows the open voltage measurement results for each method. AgO obtained using recipes 1 and 2 exhibited a higher open voltage potential than AgO directly deposited onto the substrate by reactive sputtering. On the other hand, recipes 1 and 2 displayed a low oxidation depth control and uniformity across the samples. AgO films presented a poor film quality after O 2 plasma oxidation due to the ion bombardment. Since the maximum voltage variation observed from different methods was only 70 mV, eas e of fabrication was taken as the most important factor in deciding what process to use; therefore, reactive sputtering was selected as the preferred method for the cathode material deposition since fewer steps are required for the cathode deposition. For the reactive sputtering, recipe 3 and 4 showed the same open circuit voltage. We believe that the maximum oxidation rate was achieved in recipe 3. For the microbatteries, first a 100 nm thick Ti layer was sputtered and then a 1.5 m AgO film was deposited using recipe 3. The cathode was then patterned by lift off, as shown in Fig ure 3 3 F For these microbatteries, the cathode was deposited thicker than the anode since the depletion rate of the AgO cathode is greater than that of the Al anode. A SEM image of the battery electrodes after anode and cathode deposition is shown in Fig ure 3 6 A M icrobattery Release The final step as shown in Figure 3 5 was to release the microbatteries from the Si wafer. First, the microbatteries were diced into individual batteries. Then, the top side of a few (3 to 5) batteries was attached onto a carrier wafer using PR. This allows

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31 Figure 3 5. Microbattery dicing and release by plasma etching Si substrate. A B Figure 3 6 Microbattery images A) SEM image of the microbattery before release. B) photo of the microbattery electrodes on a flexible polyimide substrate Photo s courtesy of Edgar Garay. etching the Si underneath the microbatteries without exposing the electrodes to the etchants. The carrier wafer with the microbatteries was then placed inside a STS deep reactive ion etching (DRIE) system in order to completely remove the Si (Figure 3 5) The gases for the DRIE process were SF 6 (130 sccm) and O 2 (13 sccm). The 13.5 6 MHz coil power was set to 600 W and the platen power was set to 12 W. The etching time for the Si had to be carefully controlled since the etchant gases could also attack the polyimide layer. Fig ure 3 6 B shows an image of the microbattery electrodes after

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32 release. As an example of future applications, the microbattery was attached to a g elatin capsule, as shown in Figure 3 7 Figure 3 7. Microbattery electrodes on a polyimide substrate attached to a gelatin capsule. Photo courtesy of E dgar Garay.

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33 CHAPTER 4 RESULTS AND DISCUSSION Microbattery Structure and Composition The microstructure and composition of the battery anode and cathode were inspected using a FEI Nova NanoSEM 430 field emission scanning electron microscope ( SEM). We analyzed the chemical composition by using the energy dispersive x ray spectroscopy (XEDS) abilities of the SEM. Fig ure 4 1A shows the XEDS spectrum and microstructure of the Al anode. The main component of the anode is Al, with some t races of Cu, Ti, and Si. These traces are picked up by the x ray detector since the x ray spectrum is collected from a volume sample of the anode that contains Cu, Ti, an d Si underneath the Al. Figure 4 1B illustrates the cathode x ray spectrum and the AgO surface morphology. The x ray spectrum provides evidence of the Ag oxidation using reactive sputtering, as described before. From the SEM image of the anode, the average AgO particle radius is 50 nm. This small grain structure increases the surface area t o volume ratio, increasing the reaction surface of the AgO with the electrolyte. Electrical Characterization All microbatteries were tested using a resistance static method by using different resistor values as the load. DC voltage measurements were perfor med using an Agilent HP 34401A digital multimeter. The digital multimeter was connected to a computer in order to save the data every second using a LabVIEW routine. The microbatteries were activated by micropipetting 8 L of the target fluid. Aqueous NaOH blood, urine, and saliva were used as the activation fluid for the experiments. All measurements were performed at room temperature.

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34 A B Figur e 4 1. XEDS spectrum and SEM microgr aph s. A) Al anode. B ) AgO cathode.

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35 Sodium Hydroxide Electrolyte The output voltage of all 7 microbattery types was initially measured using a 1M battery capacity was calculated and analyzed as a function of the el ectrode finger spacing ( batteries S45, S60, and S75) and finger width (batteries W45, W60, AND W75 ) and compared to the performance of battery SW 30, which is taken to be the reference battery. Fig ure 4 2A shows the preliminary results obtained for the output voltage of SW30 and S 45, S60, and S75 The capacity was calculated using E quation 2 1 ; these results are shown in Table 4 1 The maximum output voltage obtained for the microbatteries activated using NaOH was 1.7 4 V. We considered 0. 2 V as the lower limit of the operational r ange of the microbattery. From the experimental data obtained, we observed that the microbattery capacity increased as the electrode finger spacing increased The battery capacity for SW30, S45, S60, and S75 ranged from 1.41 to 5.75 Ah Decreasing the spacing between fingers from 75 m to 30 m has no apparent benefits when discharging the battery at a maximum current density of 0.5 mA/cm2 and maximum load current of 17 A. We expect that the internal resistance of the microbattery woul d decrease as the electrode finger spacing is reduced, thus improving the capacity and performance of the microbattery. However, the load current has an important role in the performance of the microbattery. For low load currents, electrode corrosion due t o the electrolyte is the main parasitic electrochemical reactions responsible for the lower capacity obtained in our experiments; therefore, capacity studies should characteri ze the current load at which the battery performance becomes a function of electrode finger spacing.

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36 A B Figure 4 2. Experimental output v oltage for microbatteries A ) Different electrode fingers spacing. B ) Different electrode finger widths.

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37 A B Figure 4 3. Microbattery experimental efficiency. A) Voltage output for different loads for battery S75 B) Experimental efficiency as a function of current density.

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38 To validate the importance of the load current in determining battery capacity, the out put voltage of battery S75 was also measured for different loads, as show in F igure 4 3 A The capacity for each load is shown in Table 4 1 Initial results show that the experimental capacity increases from 5.75 Ah to 6.87 Ah as the load current is increased from 17 A to 170 A. Also, we believe that reducing the electrolyte concentration can dramatically increase the experimental capacity of the microbatteries due to a lower self discharge rate. Fig ure 4 2 B illustrates t he output voltage measurements obtained for WS30, W45, W60, and W75 From Fig ure 4 2 B we can see that the output voltage and discharge time are approximately the same. For these microbatteries, the electrode finger width varies from 30 to 75 m in increme nts of 15 m. The width increment of the electrode fingers translates into a larger electrode area, higher theoretical capacity, and lower current density if using a load with the same resistance value. Because we used the same resistor as the load for the se experiments, the current density decreases across battery types from battery WS30 to W75 as shown in Table 4 1 The current density was calculated using the drawn electrode area. The efficiency of the microbatteries was also calculated as follows: (4 1 ) where C e and C t denote the experimental and theoretical capacity, respectively. Fig ure 4 3B shows the efficiency as a function of the current density for WS30, S75, W45, W60, and W75 From Fig ure 4 3 B it is observed that the efficiency increases

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39 proportionally to the current density. This relationship between current density and efficiency explains that the experimental capacit y for the microbatteries having a larger electrode area is comparable to the capacity of the reference microbattery, which has less than half the electrode area of the largest microbattery ( W75 ) that was fabricated in this work. Table 4 2 shows de electric al performance of the microbatteries per unit volume. Table 4 1. Electrical performance comparison for microbatteries activated using NaOH. Battery type Load (k ) Voltage Range (V) Load Current (A) a Current density (mA/cm) a Theoretical capacity (Ah) Experimental capacity (Ah) Energy (Wh) Power (W) (%) WS30 100 1.70 0.20 17 0.52 15.80 1.41 1.45 7.94 8.92 S45 100 1.71 0.20 17 0.52 15.80 1.89 1.57 5.12 11.96 S60 100 1.69 0.20 17 0.52 15.80 4.55 2.67 2.77 28.80 S75 100 1.68 0.20 17 0.52 15.80 5.75 3.18 2.55 36.39 S75 50 1.69 0.20 34 1.04 15.80 6.31 3.87 5.44 39.94 S75 10 1.66 0.20 170 5.21 15.80 6.87 8.79 108.05 43.48 W45 100 1.72 0.20 17 0.35 23.46 2.22 1.9 0 5.65 9.46 W60 100 1.74 0.20 17 0.26 31.07 1.80 1.72 7.32 5.79 W75 100 1.70 0.20 17 0.21 38.73 1.96 1.52 4.42 5.06 a Maximum value measured Table 4 2 Electrical performance of microbatteries as a function of area and volume Battery Type Load (k Area (cm) Electrode Thickness (m) Areal Capacity (Ah/cm) Energy Density (Wh/cmm) Power Density (W/cmm) WS 30 100 0.1264 1.5 11.16 7.65 41.88 S45 100 0.1582 1.5 11.95 6.62 21.58 S60 100 0.1892 1.5 24.05 9.41 9.76 S75 100 0.2206 1.5 26.07 9.61 7.71 S75 50 0.2206 1.5 28.60 11.70 16.44 S75 10 0.2206 1.5 31.14 26.56 326.53 W45 100 0.1582 1.5 14.03 8.01 23.81 W60 100 0.19 1.5 9.47 6.04 25.68 W75 100 0.2218 1.5 8.84 4.57 13.29

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40 Table 4 3 Capacity of microbatteries activated using physiological fluids a Maximum value measured Table 4 4 Electrical performance of microbatteries activated using physiological fluids as a function of area and volume Fluid Battery Type Load (k Area (cm) Electrode Thickness (m) Areal Capacity (Ah/cm) Energy Density (Wh /cmm) Power Density (W/cmm) Urine S45 50 0. 1582 1.5 44.50 19.60 35.44 Saliva S45 50 0.1582 1.5 32.43 12.09 22.38 Blood S 45 50 0. 1582 1.5 28.38 13.49 40.67 Blood S 60 10 0. 1892 1.5 36.05 14.41 117.51 Blood S 60 1 0. 1892 1.5 37.90 9.80 476.11 Microbattery Activated by Biofluids The microbatteries were further tested using blood, urine, and saliva as the activation electrolyte (Table 4 3) which are 3 of the most commonly used physiological fluids in health screening. Figure 4 4 and 4 5 shows a plot of the experimental data obtained for the output voltage of microbattery S45 and S60 For these experiments, 8 L of the target fluid were micro pipetted to the surface of the battery From Figure 4 5 A the maximum voltage output measured was 0.85 V when using blood as the activation used as the load in these experiments. When using urine a s the electrolyte and taking 0.2 V as the cut off voltage, the maxim um discharge time obtained for the microbattery was close to 35 minutes. For blood and saliva, the discharge times where F luid Battery type Load (k ) Voltage Range (V) Load Current (A) a Current density (mA/cm) a Theoretical capacity (Ah) C apacity (Ah) Energy (Wh) Power (W) (%) Urine S45 50 0.80 0.20 16 0.49 15.80 7.04 4.65 8.41 44.56 Saliva S45 50 0.80 0.20 16 0.49 15.80 5.13 2.87 5.31 32.47 Blood S45 50 0.85 0.20 17 0.52 15.80 4.49 3.20 9.65 28.42 Blood S60 10 0.75 0.20 75 2.30 15.80 6.82 4.09 33.35 43.16 Blood S60 1 0.55 0.20 550 17.03 15.80 7.17 2.78 135.12 45.38

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41 A B Figure 4 4. Voltage output for microbatteries activa ted using different electrolytes. A) Battery activated using urine. B) Battery activated suing s aliva

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42 A B Figure 4 5 V oltage output for microbattery type s S60 and S45 activa ted using blood A) Output for S45 u s ing 50 k B) Output for S60 using different loads.

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43 Figure 4 6 Ragone plot comparing the performance of our microbatteries with previously published batteries and commercial technologies close to 20 minutes. The maximum exper imental capacity obtained was 7 17 Ah when using blood as the activation fluid. The smallest resistance value used in our For this case, the operating time of the battery was less than 2 minutes and the maximum output voltage was 0.55 V, as shown in Fig ure 4 5B When using a load value of electrochemical resistance but by the internal ohmic loses as well. Additionally, we observed that in the case of physiological fluids, the discharge time of the microbattery

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44 Table 4 5 Performance comparison between our microbatteries and previously published microbatteries Chemistry Type Electrode Thickness (m) Area (cm) Flexible Voltage Range (V) Capacity (Ah) Areal Capacity (Ah/cm) Energy Density (Wh/cmm) Power Density (W/cmm) S45 Al AgO Urine On demand 1.5 0.1582 Yes 0.8 0.2 7.04 44.50 19.59 35.44 S60 Al AgO Blood On demand 1.5 0.1892 Yes 0.6 0.2 7.17 37.90 9.80 476.11 S75 Al AgO NaOH On demand 1.5 0.2206 Yes 1.7 0.2 15.80 31.14 26.56 326.53 Ref. 11 Ni Zn Rechargeable 200 0.25 No 1.7 1.3 0.63 2.50 0.01 0.17 Ref. 10 MCMB MoOS Rechargeable 500 1.33 No 2.2 1.3 2660.00 2000.00 7.00 0.70 Ref. 10 MCMB MoOS Rechargeable 500 1.33 No 2.2 1.3 n/r n/r 2.31 3.50 Ref. 26 Carbon PPYDBS Rechargeable 65 1 No 3.8 2.2 10.60 10.60 0.33 2.77 Ref. 27 LiCoO2 Li4Mn5O12 Rechargeable 180 27 No 1.2 864.00 32.00 0.17 0.04 Ref. 28 NiSn LMO Rechargeable 15 0.02 No 4.0 2.0 1.67 83.50 15.00 23.00 Ref. 28 NiSn LMO Rechargeable 12.6 0.017 No 4.0 2.0 0.05 3.02 0.60 7400.00 Ref. 36 AgO Zn Rechargeable 25 0.02 No 1.6 0.90 2.75 137.50 8.52 7.74 Ref. 21 Au Zn H2SO4 On Demand 1000 0.01 No 0.9 0.1 3.66 366.00 0.20 3.05 Ref. 25 AgCl Mg Water On demand 20 1.44 No 1.6 0.4 1260.00 875.00 2.10 2.10 Ref. 22 Mg CuCl Urine On demand 7000 18 No 1.4 0.6 n/r n/r n/r n/r Ref. 24 Pt Zn Gastric fluid On demand 2000 1.2 No 0.7 0.1 190.00 158.33 0.04 0.13

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45 was related to the time it took for the fluid to completely dry. Replenishing the activation fluid could help extend the theoretical capacity and discharge time of the microbatteries when using physiological fluids. Tabulated results of the electrical perform ance per unit volume are shown in Table 4 4. Volumetric electrical performance of batteries at the microscale needs to be considered because of the inherent space constraint of biomedical microsystems. Over the past decade, researchers have focused on inc reasing the areal energy density of microbatteries rather than volumetric energy density by creating complex geometries with high aspect ratios. The result s are microbatteries fabricated with complex methods that have an extremely low volumetric energy and power densities. Table 4 5 and Figure 4 6 present a comparison of the volumetric energy density and power density between our microbatteries and previously p microbatteries. The power density of our microbatteries is greater than the best published microb atteries except one but u nlike other published microbatteries, our batteries achieve a high volumetric power density without sacrificing energy density. Conclusions In response to the need for power sources that could be used in disposable, smart, and on demand electronic microsystems for the medical and biological fields, we have developed a unique microfabrication process using conventional MEMS techniques to fabric ate a flexible microbattery. In this project, we designed, fabricated, and tested seven microbatteries having different footprint areas. The smallest microbattery measured 2.6 mm in length, 4.86 mm in width, and 8 m in thickness. Aluminum was selected as the anode, silver oxide as the cathode, and polyimide as the flexible substrate. In this initial prototype, we have demonstrated that these

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46 microbatteries can be activated with a wide range of physiological fluids, such as blood, urine, and saliva for on d emand operation. Voltage output measurements indicated that these microbatteries achieved a maximum output voltage of 1.75 V, capacity of 7 .1 7 Ah, load current of 0.55 mA, and a maximum efficiency of 4 6 %. We anticipate that the efficiency of the battery can be improved significantly by refreshing the activation fluid and using a load current that maximizes the capacity of the battery. Future studies will focus on improving battery efficiency and crating battery circuit models that will help in the design of application specific integrated circuits. Additional efforts will be directed towards developing viable methods for integrating ou r microbattery with CMOS integrated circuits in order to develop microsystems for biomedical applications.

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47 LIST OF REFERENCES [1] R. Dreslinski, M. Wieckowski, D. Blaauw, D. Sylvester, and T. Mudge, "Near Threshold Computing: Reclaiming Moore's Law Through Energy Efficient Integrated Circuits," Proceedings of the Ieee, vol. 98, pp. 253 266, F eb 2010. [2] R. Bashirullah, "Wireless Imp lants," Ieee Microwave Magazine, vol. 11, pp. S14 S23, D ec 2010. [3] J. Rabaey, J. Ammer, B. Otis, E. Burghardt, Y. Chee, N. Pletcher et al. "Ultra low power design The roadmap to disappearing electronics and ambient intelligence," Ieee Circuits & Devi ces, vol. 22, pp. 23 29, J ul 2006. [4] M. Fojtik, D. Kim, G. Chen, Y. Lin, D. Fick, J. Park et al. "A Millimeter Scale Energy Autonomous Sensor System With Stacked Battery and Solar Cells," Ieee Journal of Solid State Circuits, vol. 48, pp. 801 813, M ar 2013. [5] H. Yu, G. Irby, D. Peterson, M. Nguyen, G. Flores, N. Euliano et al. "Printed capsule antenna for medication compliance monitoring," Electronics Letters, vol. 43, pp. 1179 1181, Oct 2007. [6] H. Tao, M. Brenckle, M. Yang, J. Zhang, M. Liu, S. S iebert et al. "Silk Based Conformal, Adhesive, Edible Food Sensors," Advanced Materials, vol. 24, pp. 1067 1072, F eb 2012. [7] L. DiCarlo, "Role for direct electronic verification of pharmaceutical ingestion in pharmaceutical development," Contemporary C linical Trials, vol. 33, pp. 593 600, Jul 2012. [8] C. Chin, V. Linder, and S. Sia, "Commercialization of microfluidic point of care diagnostic devices," Lab on a Chip, vol. 12, pp. 2118 2134, 2012 [9] G. Teixidor, R. Zaouk, B. Park, and M. Madou, "Fabric ation and characterization of three dimensional carbon electrodes for lithium ion batteries," Journal of Power Sources, vol. 183, pp. 730 740, S ep 2008. [10] M. Nathan, D. Golodnitsky, V. Yufit, E. Strauss, T. Ripenbein, I. Shechtman et al. "Three dimens ional thin film Li ion microbatteries for autonomous MEMS," Journal of Microelectromechanical Systems, vol. 14, pp. 879 885, O ct 2005. [11] F. Chamran, Y. Yeh, H. Min, B. Dunn, and C. Kim, "Fabrication of high aspect ratio electrode arrays for three dimens ional microbatteries," Journal of Microelectromechanical Systems, vol. 16, pp. 844 852, A ug 2007. [12] V. Lifton, S. Simon, J. Holmqvist, T. Ebefors, D. Jansson, and N. Svedin, "Design and Fabrication of Addressable Microfluidic Energy Storage MEMS Device, Journal of Microelectromechanical Systems, vol. 21, pp. 1392 1401, D ec 2012.

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48 [13] A. Cardenas Valencia, C. Biver, and L. Langebrake, "Reserve, thin form factor, hypochlorite based cells for powering portable systems: Manufacture (including MEMS processes ), performance and characterization," Journal of Power Sources, vol. 166, pp. 273 283, M ar 2007. [14] P. Humble, J. Harb, and R. LaFollette, "Microscopic nickel zinc batteries for use in autonomous microsystems," Journal of the Electrochemical Society, vol 148, pp. A1357 A1361, D ec 2001. [15] C. Ho, J. Evans, and P. Wright, "Direct write dispenser printing of a zinc microbattery with an ionic liquid gel electrolyte," Journal of Micromechanics and Microengineering, vol. 20, O ct 2010. [16] C. Ho, K. Murata, D. Steingart, J. Evans, and P. Wright, "A super ink jet printed zinc silver 3D microbattery," Journal of Micromechanics and Microengineering, vol. 19, S ep 2009. [17] K. Braam, S. Volkman, and V. Subramanian, "Characterization and optimiza tion of a printed, primary silver zinc battery," Journal of Power Sources, vol. 199, pp. 367 372, F eb 2012. [18] A. Armutlulu, Y. Fang, S. Kim, C. Ji, S. Allen, and M. Allen, "A MEMS enabled 3D zinc air microbattery with improved discharge characteristics based on a multilayer metallic substructure," Journal of Micromechanics and Microengineering, vol. 21, O ct 2011. [19] J. Song, X. Yang, S. Zeng, M. Cai, L. Zhang, Q. Dong et al. "Solid state microscale lithium batteries prepared with microfabrication pro cesses," Journal of Micromechanics and Microengineering, vol. 19, A pr 2009. [20] W. West, J. Whitacre, V. White, and B. Ratnakumar, "Fabrication and testing of all solid state microscale lithium batteries for microspacecraft applications," Journal of Micro mechanics and Microengineering, vol. 12, pp. 58 62, J an 2002. [21] K. Lee and L. Lin, "Electrolyte based on demand and disposable microbattery," Journal of Microelectromechanical Systems, vol. 12, pp. 840 847, D ec 2003. [22] K. Lee, "Urine activated paper batteries for biosystems," Journal of Micromechanics and Microengineering, vol. 15, pp. S210 S214, Sep 2005. [23] K. Lee, "Two step activation of paper batteries for high power generation: design and fabrication of biofluid and water activated paper batte ries," Journal of Micromechanics and Microengineering, vol. 16, pp. 2312 2317, N ov 2006. [24] H. Jimbo and N. Miki, "Gastric fluid utilizing micro battery for micro medical devices," Sensors and Actuators B Chemical, vol. 134, pp. 219 224, Aug 2008.

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49 [25] F Sammoura, K. Lee, and L. Lin, "Water activated disposable and long shelf life microbatteries," Sensors and Actuators a Physical, vol. 111, pp. 79 86, M ar 2004. [26] H. S. Min, B. Y. Park, L. Taherabadi, C. L. Wang, Y. Yeh, R. Zaouk et al. "Fabrication and properties of a carbon/polypyrrole three dimensional microbattery," Journal of Power Sources, vol. 178, pp. 795 800, Apr 2008. [27] M. Kotobuki, Y. Suzuki, H. Munakata, K. Kanamura, Y. Sato, K. Yamamoto et al. "Effect of sol composition on solid electrode/solid electrolyte interface for all solid state lithium ion battery," Electrochimica Acta, vol. 56, pp. 1023 1029, Jan 2011. [28] J. H. Pikul, H. G. Zhang, J. Cho, P. V. Braun, and W. P. King, "High power lit hium ion microbatteries from interdigitated three dimensional bicontinuous nanoporous electrodes," Nature Communications, vol. 4, Apr 2013. [29] H. Kim, R. Auyeung, and A. Pique, "Laser printed thick film electrodes for solid state rechargeable Li ion micr obatteries," Journal of Power Sources, vol. 165, pp. 413 419, F eb 2007. [30] S. D. Senturia, Microsystem design Boston: Kluwer Academic Publishers, 2001. [31] Q. Li and N. Bjerrum, "Aluminum as anode for energy storage and conversion: a review," Journal o f Power Sources, vol. 110, pp. 1 10, J ul 2002. [32] H. Liu, X. Xia, and Z. Guo, "A novel silver oxide electrode and its charge discharge performance," Journal of Applied Electrochemistry, vol. 32, pp. 275 279, M ar 2002. [33] X. Jin and J. Lu, "The potentia l valleys of silver oxide electrodes during pulse discharge," Journal of Power Sources, vol. 104, pp. 253 259, F eb 2002. [34] T. B. Reddy and D. Linden, Linden's handbook of batteries 4th ed. New York: McGraw Hill, 2011. [35] S. Pal and H. Xie, "Fabricati on of robust electrothermal MEMS devices using aluminum tungsten bimorphs and polyimide thermal isolation," Journal of Micromechanics and Microengineering, vol. 22, Nov 2012. [36] F. Albano, Y. Lin, D. Blaauw, D. Sylvester, K. Wise, and A. Sastry, "A fully integrated microbattery for an implantable microelectromechanical system," Journal of Power Sources, vol. 185, pp. 1524 1532, D ec 2008.

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50 BIOGRAPHICAL SKETCH Edgar Felipe Garay was born in Cabimas, Venezuela, in 1982. He received the B.S. degree in physics, in 2009, and the B.S. degree in electrical engineering, in 2010, from Florida International University, Miami, FL, and the M.S. degree in electrical engineering from University of Florida, Gainesville, FL, in 2013. He is currently pursuing the Ph. D. degree in electrical engineering at University of Florida, Gainesville. Since 2011 he has been a research assistant at the Integrated Circuits Laboratory under the supervision of Dr. Rizwan Bashirullah. His research interest includes the fabrication of microelectromechanical systems, integrated circuit design, and their biomedical applications. Mr. Garay was awarded the Latin American Fellowship award, the Ronald E. McNair Scholars Award of Excellence, and the South East Alliance f or Graduate Education and t he Professoriat e (SEAGEP) research award.