Thermal IR detector electrode configuration

Details Thermal IR detector electrode configuration Thermal IR detector electrode configuration

1990-09-21

1992-03-10

Fields, Carolyn E.

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

G01J 510

Patent

active

050952153

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

Pyroelectric infra-red detectors and detector arrays are used in a wide variety of applications and at operating frequencies ranging from just a few hertz to several kilohertz. Various materials have been used in this application ranging from TGS crystal through PVDF polymer to various ceramic formulations. The PZ family of ceramics. in particular, is widely used in thermal infra-red detector applications.
A significant improvement in signal-to-noise ratio can be achieved by the use of material which can be made to behave as a dielectric bolometer material, for example, lead scandium tantalate (Pb.sub.2 ScTaO.sub.6). Functionally very similar to a conventional pyroelectric material, the dielectric bolometer relies upon a pyroelectric response induced by a D.C. bias field typically with a magnitude of 1-5.times.10.sup.6 Vm.sup.-1. To provide an efficient detector, the bias field should be substantially uniform in magnitude throughout the volume of the detector material. Commonly dielectric bolometers can be fabricated from ceramic formulations which mechanically are very similar to conventional pyroelectric ceramics and allow similar processing techniques to be used mechanically to thin the materials and to define suitable electrodes.
The conventional approach to detector design is to define the detector by electrode patterning on the material surfaces. Normally, the electrodes consist of two areas defined on opposing faces of the detector material one of the electrode areas supporting some form of radiation absorber structure 20 as shown in FIG. 1 of the accompanying drawings. As shown, the detector structure requires electrical contacts 10,12 to be made to both faces 14,16 of the detector material 18. Two approaches to supporting linear array detector structures are through glue bonding the detector material to a support substrate or solder bonding using solder bumps to an interconnection substrate or readout circuit. With either technology it is difficult to contact both faces of the detector, particularly if the detector material has been reticulated to improve response and reduce thermal crosstalk between adjacent elements in an array. With a pyroelectric detector, this problem can be overcome by using a compensation region designed to cancel out common mode signals such as those caused by mechanical vibration or environmental temperature change. This region is connected in series opposition with the active element and requires electrical contacts to be made to one face of the detector only.
The pyroelectric ceramic is poled uniformly and this gives an output of opposite sign for the compensation region. Such an approach cannot, however, be applied to a dielectric bolometer where the response is induced by an applied field, if the same structure were to be used with two contacts a "compensation" region would then be acting in series complement rather than series opposition.


SUMMARY OF THE INVENTION

An object of the present invention is the provision of a thermal detector having novel electrode configurations which allow the thermal IR detector structure to be defined, whilst retaining the facility to make electrical connections to one face only, of the detector material.
According to the present invention, there is provided a thermal detector of infra-red radiation comprising a layer of detector material having electrodes so arranged that both signal contacts are taken from a single face of the detector material.
In a pyroelectric detector, the active material is either polar or is poled by applying an electric field prior to use. The electrodes used for signal read-out from each element can therefore be different from any used during poling. This is not the case for dielectric bolometers as the electrical polarisation is induced during use by a bias field. The same electrodes are therefore used both for polarisation and for read-out.
The induced polarisation is temperature dependent resulting in an induced pyroelectric coefficient, having a magnitude P(E) varying with t

REFERENCES:
patent: 3453432 (1969-07-01), McHenry
patent: 3896311 (1975-07-01), Taylor et al.
patent: 4053806 (1977-10-01), Turnbull et al.
patent: 4060729 (1977-11-01), Byer et al.
patent: 4225786 (1980-09-01), Perlman
patent: 4379971 (1983-04-01), Smith et al.
patent: 4383174 (1983-05-01), Matsumura

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