Packaging influence on acceleration sensitivity of pyroelectric infrared detectors

Pyroelectric sensors are the mostly used sensor type for infrared motion detectors since they detect temperature changes and, therefore, moving objects directly and can be applied uncooled. Such sensors are also widely used for thermal imaging and remote temperature measuring. Steady-state signals can be detected only if the incident radiation is modulated or choppered by a chopper wheel. The detectivity of such sensors is the higher the thinner the sensitive element is. Unfortunately, pyroelectric materials are inherently also piezoelectrically active. Hence, forced acceleration due to the radiation modulator or outer vibration sources influences the pyroelectric detector signal. This acceleration sensitivity or "microphony" depends strongly on the packaging of the sensor chip inside the detector setup. Extensive experimental investigations were performed to study the influence of the design parameters to acceleration sensitivity of lithium tantalate single-element sensors. It could be shown that the most decisive effects are the symmetrical sensor design and both the chip and the electrode size. Softly bonded sensor chips lead also to a microphony effect increase. Experimental results were proved by finite element modeling. FE simulations require large element numbers due to the disadvantageous chip size-thickness ratio of about 100 and since the regions near the electrode edges show complicated mechanoelectrical field distributions. Finally, guidelines for the design of acceleration-insensitive detector devices have been derived.