Thermoelectricity: From Atoms to Systems

Transcription

1 Thermoelectricity: From Atoms to Systems Week 3: Thermoelectric Characterization Lecture 3.4: Thin Film Thermoelectric Characterization By Ali Shakouri Professor of Electrical and Computer Engineering Birck Nanotechnology Center Purdue University 1

2 Thin film thermal characterization Thin film (0.1-0 mm) Substrate Applications: TE material optimization Important in electronic and optoelectronic device optimization Thermal conductivity measurement Cross-Plane: (3w, laser thermoreflectance next lecture) In-Plane: need suspended structures or modeling of heat flow around point/line sources

3 Thin film electrical characterization Thin film (0.1-0 mm) Substrate Applications: Micro refrigeration TE material optimization Electrical conductivity and Seebeck measurements In-Plane: Need non-conducting substrate (difficult at high temperatures); no charge/electrical conduction at various interfaces. Substrate transfer: consider stress induced changed in electrical properties Cross-plane: Requires especially fabricated devices to confine current, low contact resistance minimum film thickness, extract substrate contributions 3

4 Measurements of substrate-removed samples Bonding, Substrate Removal, Processing J.-H. Bahk et al., J. Electron. Mater

5 3w method for thermal conductivity 3w method (Cahill, Rev. Sci. Instrum. 61, 80) Metal line L Substrate b I 0 sin(wt) Thin Film V I ~ 1w T ~ I ~ w R ~ T ~ w V~ IR ~3w T (w ) P Lk s 1 D ln b s 1 ln i w 4 Pd Lbk f See: Annual Review of Heat Transfer, Edited by Gang Chen, 013 5

6 3w method for thermal conductivity Minimum film thickness needed to separate thin film thermal resistance from substrate/interfaces ~0.3-1mm depends on the thermal conductivity of the material Need good electrical isolation between heater and thin film (challenge at high temperatures) Electrical parasitics could contribute to the 3w signal) L b V 6

7 Thin film electrical conductivity measurement J.-H Bahk, T. Favaloro and A. Shakouri, Thin film thermal characterization techniques, Annual Review of Heat Transfer, Chapter 3, 013 7

8 In-plane Seebeck/electrical conductivity J.-H Bahk, T. Favaloro and A. Shakouri, Thin film thermal characterization techniques, Annual Review of Heat Transfer, Chapter 3, 013 8

9 Cross-plane Seebeck/electrical conductivity J.-H Bahk, T. Favaloro and A. Shakouri, Annual Review of Heat Transfer, Chapter 3, 013 9

10 Cross-plane and in-plane Seebeck in thick barrier superlattices InGaAs:ErAs/InGaAlAs Enhance energy filtering by inserting InGaAlAs barriers inside ErAs:InGaAs can enhance cross-plane Seebeck by a factor of 3 Theory/Experiment (300K) Cross-plane (with filtering) 10nm InGaAlAs 0nm n-ingaas with ErAs 10nm InGaAlAs 0nm n-ingaas with ErAs In-plane Buffer layers InP substrate Zide et al, PRB 74, 05335,

11 Transient Harman Technique Total voltage: V T V R V S IR ST I Cooling power: 1 Q STI R T Seebeck voltage: STI I R VS ST S VSP Figure-of-merit: V ZT SP V I R V SJ S TI 1 S T IR V T V R V S Harman, T. C. Journal of Applied Physics 9 (1958): t 11

12 Transient Harman Technique V R +V SP -V SJ -V R +V SP -V SJ -V R -V SP -V SJ J.-H Bahk, T. Favaloro and A. Shakouri, Annual Review of Heat Transfer, Chapter 3, 013 1

13 Simultaneous S,,, ZT measurements Neck SiN Device Gold lead ErAs/InGaAlAs Gold AlN Key issues: Current injection uniformity (aspect ratio) Heat load from probes or leads Transient response in msec Courtesy: Gehong Zeng UCSB R. Singh, Z. Bian et al. Appl. Phys. Lett. 009 May; 94:

14 T (K) Finite Element Analysis of Temperature Profile Joule Heating Exp Theory Peltier Cooling R. Singh, Z. Bian et al. Appl. Phys. Lett. 009 May; 94: Distance (mm) 14

15 Self-consistent finite element thermoelectric transport Heat capacity conduction Joule Peltier Electrical field C F T T t J / ST Ohmic J / JTS Seebeck Device Neck Gold lead SiN ErAs/InGaAlAs Gold GND R. Singh, Z. Bian et al. Appl. Phys. Lett. 009 May; 94:

16 Transient S,,, ZT measurements (Harman Technique) Seebeck Voltage (mv) R. Singh and A. Shakouri, Rev. Sci. Instrum. 009; 80: K 350K 400K 450K 500K 550K 600K 650K 700K <100ns resolution up to 800K Acknowledge: ONR DURIP (Dr. Mihal Gross) Time (ms) 16

17 Extraction of Thin-film ZT Single element microrefrigerator used to extract all thermoelectric properties of 0mm films in cross-plane direction S(mV/K) (/Wcm) K (W/mK) In-plane data N/A Cross-plane (3w), 5 Finite Element R. Singh, Z. Bian et al. Appl. Phys. Lett. 009 May; 94:

18 Z-meter measurement: n- ErAs: InGaAlAs Measured parameters: Seebeck coefficient, thermal conductivity and electrical conductivity + output power and efficiency 50um thick material Fit from thin film data Reja Amatya, Katey Lo and Rajeev Ram (MIT) Z-meter data 18

19 Lecture 3.4: Summary Thin film thermal characterization (3w) Thin film electrical and Seebeck characterization (in-plane, cross-plane) Microrefrigerator/Transient Harman for ZT characterization Z-meter A. Shakouri 9/4/013 19