(Invited) Planar Thermoelectric Micro Refrigerators Based on Nanograined SiGe Thin Films

Abstract

Rapid development of modern miniaturized microelectronic and optical devices demands for low-power and fast-response on-chip refrigeration to reduce thermal noise and improve device lifetime. Thermoelectric microrefrigerators offer an attractive all-solid-state solution with many prominent merits. Conventional thermoelectric microrefrigerators widely adopt integrated-circuit (IC)-incompatible toxic heavy metal compounds as thermoelectric elements, rendering them unsuitable for on-chip integration. Here we developed free-standing planar thermoelectric microrefrigerators based on nanograined SiGe thin films. The novel support-free design and the record high performance of the nanograined SiGe thin films lead to significant improvement in the cooling performance. A maximum cooling temperature of 10.3 K together with a response time of 16 ms has been achieved in the single-stage microrefrigerator with a power consumption of 56 μW near room temperature while a maximum cooling temperature of 11.2 K can be achieved in the two-stage refrigerator with 0.41 mW input power. The cooling temperatures of the SiGe microrefrigerators also improve with the increasing ambient temperature, reaching up to 15 K and 17 K for the single and two-stage microrefrigerators respectively at 340 K. These SiGe thin-film devices can deliver cooling performances comparable to the records for traditional heavy-metal-based microrefrigerators while providing excellent IC compatibility and almost one to two orders of magnitude higher cooling temperature to power consumption ratios (184 K/mW), rendering them ideal candidates for low-power on-chip refrigeration.