1. Technical Field
The present invention relates to a thermal detector, to a thermal detector device, to an electronic instrument, and to a method of manufacturing a thermal detector device.
2. Related Art
In the field of thermal detectors, elements such as thermopiles, pyroelectric elements, and bolometers are known. A thermopile uses thermocouples to directly detect a rise in temperature in a light absorbing film in association with absorption of light.
A pyroelectric element utilizes the pyroelectric effect of a ferromagnetic body to detect a temperature rise in a light absorbing film in association with absorption of light. For example, ferroelectric PZT (lead zirconate titanate), lithium tantalate, and other such crystals with a high dielectric constant give rise to changes in the level of electrical polarization when heated or cooled. Specifically, spontaneous changes in the level of polarization arise when the temperature changes, producing changes in the level of surface charge; whereas in the absence of temperature change, the surface charge is neutralized. In association with changes in polarization conditions, pyroelectric current flow is produced due to changes in the amount of surface charge between electrodes connected to both ends of the ferroelectric crystal. By detecting this pyroelectric current, the quantity of irradiating light (infrared or the like) can be sensed.
A bolometer detects temperature rise associated with light absorption, in the form of changes in resistance of a thermosensitive resistance element, for example.
Typically, a thermal detector has a structure that lacks a cooling system. Consequently, it is necessary to have a structure whereby the element is housed in a hermetic package or otherwise situated in a reduced pressure environment, while providing thermal separation from the substrate and neighboring film to prevent as much as possible the diffusion of heat produced by received light (infrared or the like) to the surrounding area. One effective way to prevent dissipation of heat to the substrate and avoid diminished detection characteristics of a thermal detector is to employ a structure in which, for example, a cavity for thermal separation is provided between the substrate and the thermal detector element (see Japanese Laid-Open Patent Application 2000-205944 and Japanese Laid-Open Patent Application 2002-214038 for example). Japanese Laid-Open Patent Application 2000-205944 discloses a thermal type infrared array sensor having a cavity for thermal separation, and Japanese Laid-Open Patent Application 2002-214038 discloses a pyroelectric type infrared detector element having a cavity for thermal separation.
Additionally, infrared detector elements, which are one type of thermal detector element, are employed in the field of small scale elements as personal sensors for example, and in the field of large scale arrays as infrared camera devices for example. While initially developed as military technologies, in recent years application in consumer products is progressing, and various applications for infrared detection may be anticipated in the future.