Pyroelectric infrared sensor using PZT thin plate on diaphragm as sensitive elements

To improve performance characteristics of a pyro-electric infrared sensor, especially voltage responsivity (Rv), noise equivalent power (NEP), and response speed, it is necessary to reduce the heat capacity of an infrared sensing element which is made of Pb(Zr, Ti)O3 (PZT) ceramics. A new design for a sensor whose sensing element is made of a thin bulk PZT ceramic plate mounted on a diaphragm fabricated by the Si micromachining method has been proposed and its prototypes have been tested. The prototype sensor has a PZT ceramic plate which is about 10-μm thick and has a sensing area of 1 × 2 mm2. The new sensor has an Rv value of 36.3 to 37.9 mV/μW which is about five times higher than a pyroelectric sensor with a 100-μm thick PZT bulk ceramic plate. The amount of sensor noise was expected to be reduced by half. However, the amount of sensor noise increased by a factor of two. Because of the increase in the sensor noise, the values of NEP were 1.8 to 3.3 × 10−2 μW, which is a factor of two to three smaller than the NEP value of the bulk sensor. Furthermore, the rise time decreased to 31 to 35 ms, which is 10 to 20 percent shorter than that of the bulk sensor. Thus, the reduction of sensor noise will be an important challenge for the future.