Thermal analysis of pyroelectric infrared sensors fabricated by a flip-chip transfer method

A Flip-Chip Transfer (FCT) method is being developed to integrate the ferroelectric thin film with read-out integrated circuit (ROIC), in which, the performance of the ferroelectric thin film is optimized separately with IC integration. Interconnection and mechanical bonding between the ferroelectric thin film and the signal processing circuit will be established. Micromachining process is applied to release and transfer the ferroelectric thin film to ROIC chip. To improve the mechanical strength of the sensors arid reduce the "microphone effect" caused by mechanical vibration, a thin layer of underfill is applied between the ferroelectric thin film and silicon substrate. Thermal model based on matrix method of the pyroelectric IR sensors fabricated with this FCT process is established. Influences of the thermal characteristics of various materials in the structure on the responses of the IR sensors are analyzed. Results show that the silicon substrate has the strongest influence on the responsivity of the sensor in low frequency range. Thermal conductivity of the underfill dominates the responsivity at medium and high frequencies. Other factors such as the thickness of the electrodes, the absorber, and the mechanical support layers have minor effects on the responses at frequencies of interest. The analysis shows that the FCT process can be used for the development of pyroelectric IR imaging arrays. Underfill material with low thermal conductivity is desired for high performance pyroelectric IR sensors.