Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1996-01-17
1997-11-04
Fields, Carolyn E.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
G01J 534, H01L 3702
Patent
active
056843020
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a pyrodetector element which is composed of an oriented pyroelectric thin film.
2. Description of the Related Art
A pyrodetector comprises an active sensor layer which is made of a pyroelectric material which on both sides is faced with an electrode. Pyroelectric materials used include, for example, lead zirconium titanates (PZT), preferably lead titanate or organic pyroelectrics such as poly(vinylidene fluoride) (PVDF). A permanent polarization of the pyroelectric is possible in a strong electric field or is automatically established in the process of oriented growth of the pyroelectric.
Absorption of infrared radiation in a pyrodetector gives rise to a temperature increase which causes a change in the polarization of the pyroelectric material, a voltage building up which can be read off at the two electrodes. So that a maximum measured signal is obtained for a given incident radiation, it is necessary, on the one hand, to optimize the pyroelectric properties of the material. Since, on the other hand, the extent of the temperature increase caused by the absorption of the IR radiation likewise affects the size of the measured signal, pyrodetectors are additionally optimized in terms of as small a thermal capacity as possible. This is normally achieved by reducing the layer thicknesses of the detector element and by etch-back of the substrate on which the detector element is usually built up. Thus, for example, detector elements having "free-floating" polysilicon membranes at a distance of approximately 1 .mu.m from the substrate surface are known. Etching of thin silicon membranes and free-standing tongues made of silicon, and etching of troughs in the silicon substrate underneath the pyroelectric layer are likewise known. So as to etch the substrate selectively with respect to the pyroelectric layer or with respect to the first electrode layer, assembly of the detector element is preceded by building up, on the substrate, of an additional etch stop layer which, for example, is an amorphous layer of silicon dioxide or silicon nitride.
In order for pyrodetectors having good electrical properties to be obtained, which produce large currents as the measured signals, the direction of polarization of the pyroelectric should be perpendicular to the electrode faces and thus be perpendicular to the substrate surface. Since the polarization of the perovskites from the PZT family can adopt only certain directions in the crystal, the pyroelectric layer must be applied to the substrate in at least an oriented manner and, even better, epitaxially. This requires certain monocrystalline substrate materials. R. Takayama, Y. Tomita, J. Asayama, K. Nomura and H. Ogawa, "Pyroelectric Infrared Array Sensors Made of c-Axis-oriented La-modified PbTiO.sub.3 Thin Films", Sensors and Actuators, A21-A23, 508-512 (1990), disclose a pyroelectric IR detector array on the basis of c-axis-oriented lanthanum-modified lead titanate thin films (PLT). The PLT thin film is here produced by oriented growth on a magnesium oxide single crystal as the substrate. In a subsequent process step, the PLT layer is exposed by etch-back of the magnesium oxide substrate and is faced with an electrode from underneath.
A drawback of this known pyrodetector array is the complicated interconnection of the electrodes, which partially run "underneath the substrate" and which must be connected to an external read-out and analysis circuit.
U.S. Pat. No. 3,816,750 discloses a ceramic pyrodetector, fabricated by hot pressing, on the basis of lanthanum-doped lead zirconate titanate.
Material Research Symposium Proc., Vol. 200 (1990), pages 13 to 18, disclose pyroelectric layers on top of annealed quartz, which are produced by sol-gel processes.
Material Research Symposium Proc., Vol. 243 (1992), pages 107 to 112 disclose the generation of pyroelectric layers by sol-gel processes. A silicon substrate with metal electrodes is employed.
Ferroelectrics, Vol. 128 (1992), pa
REFERENCES:
patent: 3816750 (1974-06-01), Liu
patent: 4009516 (1977-03-01), Chiang et al.
patent: 5270298 (1993-12-01), Ramesh
patent: 5387459 (1995-02-01), Hung
D.B. Betts et al., "Infrared Reflection Properties of Five Types of Black Coating for Radiometric Detectors", J. Phys. E. Sci. Instrum., vol. 18, pp. 689-696, 1985.
S. Bauer et al., "A Dunne Metallfilme als Absorber in Infrarotsensoren", Phys. vol. 48, No. 4, pp. 283-284, 1992 no month.
Takayama et al., "Pyroelectric Infrared Array Sensors Made of c-Axis-oriented La-modified PbTiO.sub.3 Thin Films", Sensors and Actuators, A21-A23 (1990), pp. 508-512 no month.
Takayama et al., "Preparation and characteristics of pyroelectric infrared sensors made of c-axis oriented La-modified PbTiO.sub.3 thin films", Journal of Applied Physics, Bd. 61, Jan. 1987, New York, NY, USA, pp. 411-415.
Y. Xu et al., "Ferroelectric Thin Films on Silicon and Fused Silica Substrates by Sol-Gel Process", Mat. Res. Soc. Symp., vol. 200, 1990, pp. 13-18 no month.
A. Pignolet et al., "Pyroelectricity in (Pb.sub.0.98 Mn.sub.0.02)(Zr.sub.0.6 Ti.sub.0.4)O.sub.3 Sputtered Thin Films", Ferroelectrics, 1992, vol. 128, pp. 37-42 no month.
L. Wang et al., "Properties of Pb(Zr.sub.x Ti.sub.1-x)O.sub.3 Thin Films Prepared by R.F. Magnetron Sputtering and Heat Treatment", Mat. Res. Bull., vol. 25, 1990, pp. 1495-1501.
Bruchhaus Rainer
Wersing Wolfram
Fields Carolyn E.
Siemens Aktiengesellschaft
LandOfFree
Pyrodetector element having a pyroelectric layer produced by ori does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pyrodetector element having a pyroelectric layer produced by ori, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pyrodetector element having a pyroelectric layer produced by ori will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1835146