SANGMIN OH, Marquette University


A micro-Kelvin (∼10−6 K) resolution thermometry for resolving micro/nanoscale heat transport using a nanomechanical membrane-based device is investigated in this research. Detecting local temperatures at the micro/nanoscale requires high resolution thermometry because of the extremely low thermal transport. High resolution thermometry to resolve the smallest heat flow output can be resolved by both minimizing the thermal conductance (Gth) and achieving the highest temperature resolution (∆Tth) according to Q̇res = Gth ×∆Tres. The nanomechanical device proposed in this research is based on the membrane structure with silicon nitride (SiN) membrane. A 20 nm thick low stress SiN film is deposited on a silicon wafer by low pressure chemical vapor deposition (LPCVD) and a free-standing SiN membrane is created through the micromachining process. The SiN membrane is sealed with another SiN membrane device (500 nm thick) to form an air chamber. As the temperature in the air chamber increases, the pressure in the air chamber also increases by ideal gas law, resulting in the deflection of the SiN membrane. Thus, the temperature variation in the air chamber can be detected by measuring the displacement of the membrane deflection. The temperature resolution of the 20 nm thick SiN membrane device is directly proportional to the stiffness of the SiN membrane. The stiffness of the suspended SiN membrane is analyzed using several detailed methods based on two different load conditions. To determine the ultimate temperature resolution, the thermal conductance of the membrane device is measured by a step power response. A sub nano-Watt (0.36 nW) is measured using a Polytec MSA-100-3D laser Doppler vibrometer in an open lab environmental condition. Based on the measured power and the thermal conductance of the device, the temperature resolution is calculated as 1.3 × 10−8 K. These measured sub-nW and calculated sub-µK resolutions are suitable for studying thermal transport at the micro/nanoscale.r