Piezoresistive heat engine and refrigerator

TL;DR

This paper introduces a novel crystalline silicon piezoresistive heat engine and refrigerator at microscale, demonstrating conversion of electrical heat into mechanical work and vice versa, with potential for miniaturized thermal devices.

Contribution

It presents the first demonstration of a crystalline silicon-based piezoresistive heat engine and refrigerator operating at microscale sizes, utilizing high DC current to drive thermomechanical cycles.

Findings

Engine operates at 0.34 μm^3 size with sustained oscillations.

Engine can amplify Brownian motion below threshold.

Refrigerator mode reduces thermal fluctuations in the structure.

Abstract

Heat engines provide most of our mechanical power and are essential for transportation on macroscopic scale. However, although significant progress has been made in the miniaturization of electrostatic engines, it has proven difficult to reduce the size of liquid or gas driven heat engines below 10^7 um^3. Here we demonstrate that a crystalline silicon structure operates as a cyclic piezoresistive heat engine when it is driven by a sufficiently high DC current. A 0.34 um^3 engine beam draws heat from the DC current using the piezoresistive effect and converts it into mechanical work by expansion and contraction at different temperatures. This mechanical power drives a silicon resonator of 1.1x10^3 um^3 into sustained oscillation. Even below the oscillation threshold the engine beam continues to amplify the resonator's Brownian motion. When its thermodynamic cycle is inverted, the structure is shown to reduce these thermal fluctuations, therefore operating as a refrigerator.