Fabrication process for 256 x 256 bolometer-type uncooled infrared detector

Abstract

A process for fabricating a monolithic 256 X 256 bolometer-type uncooled IR detector array is presented that utilizes surface micromachining technology. Each pixel of the device is composed of two parts, a silicon readout integrated circuit in the lower part and suspended microbridge structures in the upper part. The device is based on vanadium oxide bolometer films, which typically exhibit a temperature coefficient of resistance of -2 percent K. The vanadium oxide film is subject to damage, especially during wet etching of the sacrificial layer. Hence, the material and deposition process of the passivation layer for vanadium oxide film were investigated toward attaining a damage-free and flat microbridge structure. This was achieved by adjusting both the thickness of the passivation layer and the stresses in the electrode and passivation layers. The stiction problem of the microbridge structure was solved, by investigating drying conditions after etching of the sacrificial layer. Since each pixel has a cavity structure of (lambda) /4 to absorb IR radiation of the wavelength (lambda) , the spectral response of the pixel was measured in the wavelength range of 2 to 12 micrometers . The interference characteristics can clearly be seen. From responsivity measurements both in vacuum and at one atmosphere, the thermal time constant, thermal mass, and thermal conductance were estimated.