A ferroelectric / pyroelectric sensor employs a technique for determining a charge output of a ferroelectric scene element of the sensor by measuring the
hysteresis loop output of the scene element several times during a particular
time frame for the same temperature. An external AC
signal is applied to the ferroelectric scene element to cause the
hysteresis loop output from the element to switch polarization. Charge integration circuitry, such as a combination output
capacitor and
operational amplifier, is employed to measure the charge from the scene element. Preferably, the ferroelectric of the scene element is made of an economical and responsive
strontium bismuth tantalate, SBT, or derivative thereof, disposed directly between top and bottom electrodes. Because of the frequency characteristics of the sensor, created by the external AC
signal, the element need not be thermally isolated from the
silicon substrate by a traditional
air bridge, which is difficult to manufacture, and instead is preferably thermally isolated by spin-on-glass, SOG. To prevent saturation of an output
signal voltage of the sensor by excessive charge accumulation in an output
capacitor, the sensor preferably has a reference element configured electrically in parallel with the scene element. When the
voltage of the AC signal is negative the output
capacitor is discharged by flowing current through the reference element thus interrogating the polarization of the reference element which is compared to and subtracted from the polarization of the scene element for each cycle. The polarization difference measured for each cycle over a set time period are summed by an integrating
amplifier to produce a signal output
voltage.