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Carbon-MEMS Architectures for 3D Micro-batteries

Carbon-MEMS Architectures for 3D Micro-batteries. Marc Madou Department of Mechanical and Aerospace Engineering, UCI ECS, Orlando, October 14, 2003. Madou group/UCI: C.L.Wang L.Taherabadi G.Y.Jia S.Kassegne A.Randhawa. Dunn group/UCLA : C.W.Kwon George Baure Tim Yeh.

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Carbon-MEMS Architectures for 3D Micro-batteries

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  1. Carbon-MEMS Architectures for 3D Micro-batteries Marc Madou Department of Mechanical and Aerospace Engineering, UCI ECS, Orlando, October 14, 2003

  2. Madou group/UCI: C.L.Wang L.Taherabadi G.Y.Jia S.Kassegne A.Randhawa Dunn group/UCLA: C.W.Kwon George Baure Tim Yeh

  3. Organization of this Talk • Intro • Earlier Results • Advantages of C-MEMS Batteries • Recent Results • Conclusions

  4. Intro: Batteries in Our Daily Life Miniature portable electronic devices • Cardiac pacemakers • Hearing aids • Smart cards • Personal gas monitors • MEMS devices • Embedded monitors • Remote sensors with RF capability Advanced Microbattery Availability ofnew materials : photoresists Development ofmicromachined battery designs : C- MEMS

  5. Intro: Current State of Art and Problem Definition • Lithium-based secondary batteries - high values of practical specific energies(150 Whkg-1) and energy densities (220 WhL-1)-- vs. gasoline (3000 Whkg-1) • Highly ordered graphite, hard carbon and soft carbon serve as host materials for lithium storage in commercial Li batteries (anode). • Reported values of energy density are generally based on the performance of larger cells with capacities of up to several ampere-hours. For small microbatteries the achievable power and energy densities are diminished because the packaging and internal hardware will determine the size and mass of battery  New manufacturing methods and new materials are needed.

  6. Intro: Our Approach • Carbon-microelectromechanical system (C-MEMS) technology provides both the material and manufacturing solution to this battery miniaturization problem. • We overcome the size and energy density deficiencies of 2D batteries by creating three dimensional(3D) microelectrode arrays by patterning photoresists and converting those patterns into new battery and battery array designs.

  7. Vacuum Ceramic tube N2 or forming gas Exhaust gas Quartz tube Earlier Results: What is C-MEMS? (a) WEBB #40 vacuum furnace (b) Inert gas furnace

  8. Earlier Results: What is C-MEMS? • Photoresists are patterned by (e.g, using photolithography) and pyrolyzed in an inert environment (e.g., vacuum) to yield carbon films and microstructures. • In earlier work we demonstrated that photoresist derived carbon electrodes exhibit kinetics comparable to glassy carbon for selected electrochemical reactions in aqueous and nonaqueous electrolytes (Madou et al, JECS).

  9. Earlier Results: Sheet Resistance and TEM Photos of Pyrolyzed Photoresist Sheet Resistance (Ohm/square) Positive photoresist Negative photoresist Temperature (°C) Sheet resistance vs temperature of heat treatment for AZ-4330 and OCG-825 resists S.Rnaganathan, M.Madou et.al, ”Photoresist derived carbon for microelectromechanical systems”

  10. Earlier Results: 3D Structure-Micro Patterning of Conductive Polymers (e.g., PAN and PPY) M.Madou. ,”Fundamentals of Microfabrication”

  11. Earlier Results: Electric Field and Current modeling for 3D carbon electrodes of microbatteries (Top panels) Schematic diagram of 3-D cylindrical battery arrays in parallel row (left) and alternating anode/cathode (right) configurations. (Middle panels) Isopotential lines between cathode (C) and anode (A) for unit battery cells. (Bottom panel) Current densities (in arbitrary units, a.u.) at the electrode surfaces as a function of the angle (see middle panel for definition of q) ( Dunn et al.)  make as high an aspect ratio electrodes as possible!!!!

  12. Advantages of C-MEMS Batteries • High current density on a small foot-print, • Anodes and cathodes in the same plane (easier to manufacture), • The current collectors and electrode posts are all fabricated in the same simple one -step process, • Si substrate is compatible with further CMOS integration  CMOS Battery unit Smart switchable battery arrays: baxels are addressable just like pixels: in a serial arrangement, voltages add up; in a parallel arrangement, currents add up

  13. Advantages of C-MEMS Batteries • High repeatability of batch microfabrication and the C-MEMS material, • Customized design possible, • Battery arrays may be stacked using the latest space efficient IC packaging techniques (e.g., double sided alignement).

  14. Advantages of C-MEMS Batteries • Interdigitated fields of anode and cathode poles, • One planar substrate with electrolyte in between poles, • Any voltage/current combination can be achieved on demand.

  15. Recent Results • Microfabrication --- • We developed high aspect ratio 3D carbon posts ( >> 10 (> 40 is possible)) in different types of array configurations • C-MEMS interconnects --- an all C design, , C and Au and a C and SiO2 design • Electrochemical tests-- Li charge/discharge processes in pyrolyzed arrays of photoresist posts

  16. How to Build High Aspect-ratio3D Carbon Posts? Build 3D photoresist structure by photolithography • Positive photoresist (AZ4620, SP 1827) • Multi-exposure and multi-developing for multilayer photoresist • Embedded masks for multilayer photoresist • Molds • Negative photoresist (SU-8 100) Pyrolysis of photoresist Vacuum or forming gas (95% N2 and 5% H2) atmosphere, 9000C

  17. Si SiO2 PR Au Positive Photoresist (1) :Multi-exposure and multi-developing • Problem: • bottom layer: over baked • surface layer: over exposed and developed • Difficult to get high aspect ratio straight posts

  18. Positive Photoresist (2): Embedded masks UV mask developing wet etching repeat exposure/ developing/etching UV + developing wet etching Si PR Au Ti or Si or Cr

  19. PR/Au/PR/Si(200Å)/PR Positive Photoresist (2): Embedded masks PR/Cr(1000Å)/PR Problem: Before pyrolysis: a lot of bubbles on surface After pyrolysis: peeling

  20. PR Positive Photoresist (3): Molds Before spin coating PR after spin coating PR

  21. High Aspect-ratio Carbon Posts Derived from SU-8 : Direct pyrolysis

  22. SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si before

  23. SU-8/SiO2 or SiN/Si before

  24. SU-8/Au(3000Å)/Ti(200Å)/SiO2/Si after

  25. - + - + - - + Current distribution on a section of electrode array SU-8/SiO2/Si after

  26. Electrochemical Tests Teflon Li 1M LiClO4 in DMC sample

  27. Electrochemical Tests Graph from UCLA microbattery group • Flat C-MEMS • Two-electrode configuration (reference /counter electrode is a lithium metal foil (Aldrich 99.99 %). The WE is C-MEMS. Electrolyte was 1M LiClO4 in dimethyl carbonate (DMC). Carbon sample area measured was ~ 0.4 cm2, and a constant current of 5 mA was applied between 0.005 ~ 3 V vs. Li+/Li. The first capacity is ~ 8.5µAh and the second is ~ 5.5 µAh. The process is quite reversible.Assuming the density of carbon is 2 g/cm3, the estimated specific reversible and irreversible capacities are 49 and 27 mAh/g, respectively.

  28. carbon Si/ SiO2 Electrochemical Tests • First five cycles of discharge/charge experiments. The first discharge capacity is ~ 233 Ah and the second is ~ 110 Ah. The process is quite reversible after the first cycle. • The sample is composed of columnar posts with a diameter of 50 um and spacing of 50 um. • If the second discharge capacity is taken as a reversible capacity, the specific reversible and irreversible capacities are 1410 and 1577 mAh/g, respectively. The reversible capacity is too large compared to those of say soft carbon (~ 150 mAh/g), therefore there must be huge contribution of carbon underneath the micropattern and/or outside the measuring window. Anyway, this type of micropatterned sample seems electrochemically active and reversible, which proves the validity of the approach. Graph from UCLA microbattery group

  29. After Electrochemical Tests Positive PR, 90x90 arrays: Ø 100µm, thickness: 4µm Before 1st capacity: 0.138mAh(294mAh/g) 2nd capacity: 0.0104mAh (22.3mAh/g)

  30. Electrochemical Tests 1st capacity: 3.122mAh(153.3mAh/g) 2nd capacity: 0.190mAh(9.33mAh/g)

  31. Conclusions • We successfully made high aspect ratio (> 10:1) carbon posts by pyrolysis from negative photoresists in a simple one-step process • We can make baxel arrays in any type of configuration • Electrochemical tests demonstrate that these C-MEMS electrodes can be charged/discharged with Li • A C-MEMS battery approach has the potential to solve both manufacturing and materials problems all at once

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