Microfabricated Arrays Of Peltier Coolers For Cryobiology

1. Microfabricated Arrays Of Peltier Coolers For Cryobiology Aparna Prabhakar Advisor: Dr. Ram Devireddy ALL THE BEST !!!! just don’t get nervous………… ? ALSO DON”T FORGET TO INTRODUCE URSELF!!!!ALL THE BEST !!!! just don’t get nervous………… ? ALSO DON”T FORGET TO INTRODUCE URSELF!!!!

2. Overview Research Objective Experimental Techniques Mathematical Model Future work

3. Research Objective Enable highly localized control of temperature in a native or artificial tissue system. Enable further usage of low temperatures in biological systems. HOW TO DO SO? Develop an array of micro thermoelectric coolers (TECs). The organization of the device will consist of an array of 100 TECs that will be formed by electrodeposition of the proper materials (bismuth, Bi and telluride, Te). Within the array, the coolers will be interspersed to enable each one to be individually addressable and with each individual TEC having an n-type and p-type leg elements. These arrays of TECs will be embedded in polymethylmethacrylate (PMMA) matrix to improve insulation and will be situated under the tissue system to be cooled. PMMA sheet will provide an interface between the cooler and the embedded cells.The organization of the device will consist of an array of 100 TECs that will be formed by electrodeposition of the proper materials (bismuth, Bi and telluride, Te). Within the array, the coolers will be interspersed to enable each one to be individually addressable and with each individual TEC having an n-type and p-type leg elements. These arrays of TECs will be embedded in polymethylmethacrylate (PMMA) matrix to improve insulation and will be situated under the tissue system to be cooled. PMMA sheet will provide an interface between the cooler and the embedded cells.

4. Flow Chart of the Process Now to help u visualize better, we can divide this research into various stages… the 1st stage involved the intial steps of …..the second stage … Now to help u visualize better, we can divide this research into various stages… the 1st stage involved the intial steps of …..the second stage …

5. Principle of TEC Based on Peltier effect – “If a current passes through a thermocouple, the temperature of one junction increases and the temperature of the other decreases, so that heat is transferred from one junction to the other.”

6. Electrodeposition Electrodeposition is used to produce p and n-type semiconductors. Rota-Hull Device allows testing of many current densities in one experiment. Remember to mention Bi-Te material selection! Remember to mention Bi-Te material selection!

7. Electrodeposition The lower the pH, the less time the tellurium takes to dissolve. At least 36h was needed to obtain a clear transparent solution. The p-type Bi-Te alloy is bismuth rich whereas the n-type is tellurium rich while the stoichiometric composition ratio, Bi2Te3 (Bi% - 52, Te% - 48) is electronically neutral. Just give a brief explanation of the rull –hull set upJust give a brief explanation of the rull –hull set up

8. Final Deposition Characteristics

9. Electrodeposition Results Deposited films displayed desirable characteristics of metallic, regular pearl-gray deposition. The current densities needed to get the desired p and n-type semiconductor were observed to be in the range of 0.3 to 7.5 mA/cm2 with corresponding growth rates of 0.34 to 3.9 µm. Indicates p-type material would be obtained for values of E < 0.23V and n-type for values of E > 0.23V. The Bi-Te system is kinetically controlled, i.e. they do not reach a point of limiting current. Te was always observed to be of higher concentration than Bi. Experiments have shown that it is feasible to produce the TECs through electrodeposition of bismuth and telluride

10. Design Constraints TEC cross sectional area ~50?m. All the materials used should be “Biocompatible”. The area in contact with the cells should be a good conductor of heat and a bad conductor of electricity.

11. Mathematical Model Cooling parameters TEC structure Limitations: No Radiation No air conductance between the TEC legs.

12. Governing Equation

13. Mathematical Model Results Dimensions: Couple: L*b*w: 23 * 10 * 10?m Interconnects: L*b*w: 20 * 15 * 5?m Ceramic: L*b*w: 50 * 20 * 200?m Expected Performance: Effective Z of couple = 90% Z of the material. Optimum Current: 1.2mA Heat dissipated: 0.62?W Max. Temperature Drop: 11 Th=300K ; Tc = 289K Area to length factor: 4.90?m Breakdown Current: 2.5mA

14. Current Status Nano scales = 1.5*Delta T micro scales Determining parameters: - Length Factor, y=a/l. - Joules Heating Term, I2R Expected temperature drop ~ 10K. Breakdown Current: 2.5mA

15. Future Work Flat plate experiments - Composition and deposition conditions. - Relationship between the electrical and thermal properties. Fabrication of the device using multi-step LIGA process. Finalization of the wiring and the associated control system. Testing the final device.

16. Acknowledgements Dr. Ram Devireddy Dr. Murphy Dr. Podlaha-Murphy Louisiana Board Of Regents Adam Cygan All my Lab mates and friends

17. Questions?