Integrated tilt angle sensing for large displacement scanning MEMS mirrors

Fourier transform spectrometers (FTS) based on piston-scanning MEMS mirrors have clear advantages of small size and low cost. However, the performance of this type of MEMS FTS is seriously limited by the difficulty of precisely controlling the tilt angle of the MEMS mirror plate during its piston scanning. This paper reports an integrated tilt angle sensing method, which is achieved via a mixed signal integrated optoelectronic position sensor (iOE-PS) that is bonded directly on the back of an electrothermally-actuated MEMS mirror. The iOE-PS integrates a laser diode, a band-gap reference, a quadrant photo-detector (QPDs), and the QPDs' readout circuits all on a single chip. The iOE-PS has been fabricated in a 180 nm CMOS process. Experimental results show that the iOE-PS has a linear response when the MEMS mirror plate moves vertically between 1.31 mm to 1.50 mm over the iOE-PS chip; the tilt angle can be measured up to at least 5° with a resolution of 0.0067°. The iOE-PS can greatly reduce the size and complexity of MEMS mirrors-enabled systems with integrated closed-loop control capability.