Nanomechanical thermometry for probing sub-nW thermal transport.

Accurate local temperature measurement at micro and nanoscales requires thermometry with high resolution because of ultra-low thermal transport. Among the various methods for measuring temperature, optical techniques have shown the most precise temperature detection, with resolutions reaching (~10^-9 K). In this work, we present a nanomechanical device with nano-Kelvin resolution (~10^-9 K) at room temperature and 1 atm. The device uses a 20 nm thick silicon nitride (SiN) membrane, forming an air chamber as the sensing area. The presented device has a temperature sensing area >1 mm² for micro/nanoscale objects with reduced target placement constraints as the target can be placed anywhere on the >1 mm² sensing area. The temperature resolution of the SiN membrane device is determined by deflection at the center of the membrane. The temperature resolution is inversely proportional to the membrane's stiffness, as detailed through analysis and measurements of stiffness and noise equivalent temperature (NET) in the pre-stressed SiN membrane. The achievable heat flow resolution of the membrane device is 100 pW, making it suitable for examining thermal transport on micro and nanoscales.