Modeling and Characterization of MicroPirani Vacuum Gauges Manufactured by a Low-Temperature Film Transfer Process

The novelty of this paper is the proof of functional microdevice fabrication using a recently developed low-temperature transfer process. The process is based on adhesion control of molded Ni microstructures on a donor wafer by using plasma-deposited fluorocarbon films. Low-temperature adhesive bonding of the microstructures on the target wafer using benzocyclobutene sealing enables mechanical tearing off from the donor wafer. Interest of this process for manufacturing microsensors is demonstrated here in the case of microbeams used as pressure sensors based on the Pirani principle. A simple analytical model is used to estimate the electrothermal behavior of the suspended microwires as a function of the ambient gas pressure. Estimations are compared to experimental measurements performed on Ni electroplated microwires of 550-1200-μm length, 10-μm width, and 0.7-7- μm thickness characterized into a vacuum chamber. These microsensors present a maximum of sensitivity in the range of 0.1-100 mbar, which is in line with standard performances of Pirani gauges. The presented results thus demonstrate the interest of a simple film transfer process for the elaboration of 3-D functional microstructures.