Thick-film thermoelectric microdevices

Miniaturized thermoelectric devices integrated into thermal management packages and low power, high voltage, electrical power source systems are of interest for a variety of space and terrestrial applications. In spite of their relatively low energy conversion efficiency, solid-state microcoolers and microgenerators based on state-of-the-art materials offer attractive solutions to the accelerating trend towards miniaturization of electronic components and `system on a chip' concepts where the functions of sense, compute, actuate, control, communicate and power are integrated. The miniaturization of state-of-the-art thermoelectric module technology based on Bi₂Te₃ alloys is severely limited due to mechanical and manufacturing constraints. Compared to bulk technology, the key advantages of integrated microdevices designed with thousands of thermocouples are their ability to handle much higher heat fluxes (thus resulting in high power densities), their much faster response time as well as the possibility of generating high voltages under small temperature differentials. We are currently developing novel microdevices with a conventional vertically integrated configuration combining high thermal conductivity substrates such as diamond or silicon, integrated circuit technology, and electrochemical deposition of thick thermoelectric films. We report here on our progress in developing techniques for obtaining 10-50 μm thick films of p- and n-type Bi₂Te₃ alloys by electroplating through a thick photoresist template on top of patterned multilayer metallizations. This microdevice fabrication technology is now being developed for several applications, including a high cooling power density microcooler (200 W/cm²) for thermal management of power electronics and a 100 mW autonomous hybrid thermoelectric-rechargeable batteries generator using low grade waste heat. Future directions of research are also discussed.