Abstract
For sensors constructed by freestanding membranes, when the gap between a freestanding membrane and the substrate or between membranes is at micron scale, the effects of near-field radiative heat transfer on the sensors' thermal performance should be considered during sensor design. The radiative heat flux is transferred from a membrane to a plane or from a membrane to a membrane. In the current study of the near-field thermal radiation, the scanning probe technology has difficulty in making a membrane separated at micron scale parallel to a plane or another membrane. A novel MEMS (micro electromechanical system) device was developed by sacrificial layer technique in this work to realize a double parallel freestanding membrane structure. Each freestanding membrane has a platinum thin-film resistor and the distance between the two membranes is 1 μm. After evaluating the electrical and thermal characteristics of the lower freestanding membrane,experimental measurements of near-field radiative heat transfer between the lower membrane and the upper membrane were carried out by setting the lower membrane as a heat emitter and the upper membrane as a heat receiver. The near-field radiative heat transfer between the two membranes was validated by finding a larger-than-blackbody radiative heat transfer based on the experimental data.
Highlights
Freestanding micro-mechanical membrane structures have been developed and applied as a variety of sensors [1,2,3,4,5,6,7,8,9,10]
The distance between the freestanding membrane and the substrate or between two membrane is from micron to submicron scale for sensors fabricated by front-side surface micromachining techniques [16,17]
The heating power was different between DFM and SFM when heating the lower membrane to the same temperature
Summary
Freestanding micro-mechanical membrane structures have been developed and applied as a variety of sensors [1,2,3,4,5,6,7,8,9,10]. Thermal conduction and thermal radiation are two generally considered heat transfer modes of a freestanding membrane working in vacuum. The radiative heat power per unit temperature difference of the near-field radiation between two SiO2 (silicon oxide) planes has been found to be 6 nW and 18 nW at the gap of 2.5 μm and 30 nm, respectively [15]. They are higher than the 5.45 nW of the far-field radiation under the same temperature conditions. The near-field radiative heat transfer occurs at the micron or the submicron distance and brings away more heat from the freestanding membrane. The near-field radiative heat transfer mode needs to be studied to direct the structural design of the sensors
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