Niloufar Ghafouri

Low-temperature characterization and micropatterning of coevaporated Bi2Te3 and Sb2Te3 films

Thermoelectric (TE) properties of the coevaporated Bi2Te3 and Sb2Te3 films are measured from 100 to 300 K for Seebeck coefficient αS and from 5 to 300 K for electrical resistivity ρe, mobility μe, and Hall coefficient RH. For the low-temperature characterization of TE films, the conditions for coevaporation deposition of Bi, Te, and Sb to form Bi2Te3 and Sb2Te3 films are also investigated, including substrate material, substrate temperature Tsub, and elemental flux ratio (FR). The resublimation of Te occurring above 473 K significantly affects the film composition and quality. Our optimal deposition conditions for Bi2Te3 films are Tsub=533 K and FR=2.4, and those for Sb2Te3 films are Tsub=503 K and FR=3.0. The TE properties of both films are strongly temperature dependent, while Bi2Te3 films show a stronger temperature dependence than Sb2Te3 films due to different major scattering mechanisms. αS of both the coevaporated films are close to or higher than those of bulk materials, but ρe is much higher (due ...

Multistage Planar Thermoelectric Microcoolers

Many types of microsystems and microelectromechanical systems (MEMS) devices exhibit improved performance characteristics when operated below room temperature. However, designers rarely pair such devices with integrated cooling solutions because they add complexity to the system and often have power consumption which far exceeds that of the microsystem itself. We report the design, fabrication, and testing of both one- and six-stage thermoelectric (TE) microcoolers that target MEMS applications through optimization for low-power operation. Both coolers use thin-film Bi2Te3 and Sb2Te3 as the n-and p-type TE materials, respectively, and operate in a planar configuration. The six-stage cooler has demonstrated a ΔT = 22.3 °C at a power consumption of 24.8 mW, while the one-stage cooler has demonstrated a ΔT = 17.9 °C at a lower power consumption of 12.4 mW.

A micro thermoelectric energy scavenger for a hybrid insect

We report: (1) the design, fabrication, and testing results of an implantable micro-scale thermoelectric power scavenging device that utilizes the body temperature of beetles as an energy source, (2) measurements of beetle body temperature during flight and (3) the developmental stability of beetles with implanted devices. The implantable energy scavenger consists of multiple Bi2Te3 legs and long heat pipes that extend outside the beetlepsilas body to maintain a temperature difference. The device is fabricated on a flexible SU-8 substrate, has a footprint of 2times4 mm2, and is 250 mum thick. It produces a power density of 10 muW/cm2 with an 11degC DeltaT. The beetles produce an 11degC temperature difference during flight at the wing base and demonstrate a survival rate over 95% when devices are implanted in their backs during the pupa stage.

Post-CMOS FinFET Integration of Bismuth Telluride and Antimony Telluride Thin-Film-Based Thermoelectric Devices on SoI Substrate

This letter reports, for the first time, heterogeneous integration of bismuth telluride (Bi₂Te₃) and antimony telluride (Sb₂Te₃) thin-film-based thermoelectric (TE) devices on a CMOS substrate. The TE films are deposited on a silicon-on-insulator substrate with FinFETs (3-D multiple gate field effect transistors) via a characterized TE-film coevaporation and shadow-mask patterning process using predeposition surface treatment methods for reduced TE-metal contact resistance. As a demonstration vehicle, a 2 × 2 mm²-sized integrated planar thermoelectric generator (TEG) is shown to harvest 0.7 μW from 21-K temperature gradient. Transistor performance showed no significant change upon post-CMOS TEG integration, indicating, for the first time, the CMOS compatibility of the Bi₂Te₃ and Sb₂Te₃ thin films, which could be leveraged for realization of high-performance integrated micro-TE harvesters and coolers.

High-performance micro scale thermoelectric cooler: An optimized 6-stage cooler

We report the design, fabrication and testing of an optimized 6-stage planar thermoelectric (TE) micro cooler producing a ΔT = 22.3 °C at a power consumption of 26 mW, the best performance reported to date for a thermoelectric microcooler. This microcooler has a compact chip-scale design, and utilizes Bi<inf>2</inf>Te<inf>3</inf> and Sb<inf>2</inf>Te<inf>3</inf> thermoelectric thin films deposited on thermally isolating silicon oxide bridges [1]. The fabricated cooler incorporates a total of 126 thermocouples across 6-stages within a volume of 5×5×1 mm³.

A multistage in-plane micro-thermoelectric cooler

This paper presents a mutli-stage thermoelectric micro cooler designed for integration with a wide variety of MEMS devices, including MEMS resonators, which benefit from decreased phase noise at low temperatures. The cooler is fabricated using a multilayer process that allows the device to achieve thermal isolation greater than 10,000 K/W while still maintaining mechanical robustness for practical applications. Co-evaporated thin film bismuth telluride and antimony telluride are used as the thermoelectric materials. The cooler is 9 x 9 mm2 and a preliminary prototype has achieved cooling of 3.8 K, comparable to values predicted using a one-dimensional mathematical model.