Texas Instruments, in 1976, began developing a radically new thermal imaging sensor approach. Based on using the pyroelectric properties of certain ceramic materials, techniques where developed to fabricate two-dimensional arrays with enough pixels to provide adequate resolution for all but the most demanding applications. Available today from Raytheon Commercial Infrared, BST array sensor technology is widely used in commercial infrared imaging products such as Cadillac’s night vision system, the majority of fire service cameras and the PalmIR series of hand held cameras.

Pyroelectric sensors exhibit internal spontaneous electrical polarization, which can be measured as a voltage at electrodes placed on opposite faces of a sample of the ferroelectric material. At a constant temperature of the sample, this internal polarization is neutralized by mobile charges on the surface of the sample; thus there is no voltage difference measured by the electrodes. If the temperature is suddenly changes to a new value, the internal polarization will change, resulting in a measurable voltage difference. Thus pyroelectric detectors based on ferroelectric materials do not have a DC signal. The surface temperature must be modulated in time. This is usually accomplished by means of a radiation chopper. The detector’s output becomes an alternating current in the external circuit connected to opposite faces of the detector

• Greatly reduced fixed pattern noise. Microbolometer based system typically have significant fixed pattern noise that appears as rows or columns.Due to sensor signal drift an offset calibration must be performed periodically based on a number of factors. A chopper-based system effectively continuously performs this same function providing an image with very uniform flat output.
• Ambient temperature drift immunity. All uncooled thermal detector based systems are unshielded, meaning that up to 80% of the infrared radiation that reaches the detector elements comes from the lens housing and other non scene contributions. Any temperature change in the camera creates something similar to a DC level drift. Since the ferroelectric systems are AC coupled there is no need to perform any ambient temperature offset correction. This attribute has been a critical discriminator in the selection by automotive companies to use the ferroelectric uncooled thermal imaging technology in their cars.

A pixel made from a crystal of ferroelectric material such as the barium strontium titanate (BST) found in Raytheon PalmIR500 is hybridized to a CMOS multiplexer circuit mounted which is in contact with a thermal electric cooler/stabilizer. The devices temperature set point is set close to the BST crystal’s Curie temperature, or the narrow temperature band at which the crystal material exhibits the highest polarization relative to the detector’s temperature change resulting from scene illumination.
The pyroelectric effect is an electrical polarization that can be measured as a transient electrical charge on opposite faces of the crystal element. As the device reaches temperature equilibration, neutralization of the surface charge occurs. This requires the infrared radiation illuminating the infrared pixel to be modulated through the use of a chopper mechanism. The detector is hybridized to a silicon multiplexer circuit that samples the differential signals and the camera’s electronics generate the video/digital signal seen in the viewfinder or on the color LCD display