Sensor system and manufacturing process as well as...

Details Sensor system and manufacturing process as well as... Sensor system and manufacturing process as well as...

1998-08-13

2001-09-25

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S339090, C250S352000

Reexamination Certificate

active

06294787

ABSTRACT:

FIELD AND BACKGROUND
The invention concerns a sensor system as well as a manufacturing process and a self-testing process for the same. The sensor system serves for the detection of thermal radiation. Various arrangements are known for the detection of thermal radiation, especially infrared radiation (IR-radiation).
FIG.1
shows the principal construction schematically. Two (or more) sensor elements
10
are attached to a substrate
15
. An image of the thermal or IR-radiation given off by a source of thermal radiation
19
is formed on the detection surface of the sensor elements
10
, for example, by a lens
14
. The radiation is imaged by this arrangement on one of several sensor elements
10
, so that a resolution according to different spatial-angle zones is possible in proportion to the number of sensor elements
10
.
Such systems have the disadvantage that thermal inductive disturbances or cross talk can result due to heat conducted between the individual sensor elements
10
. This means that a sensor element
10
, which is not illuminated by (optically imaged) infrared radiation, will deliver a signal nevertheless, because it receives heat from neighboring sensor elements
10
which are irradiated by thermal radiation. A sensor element can be thereby warmed, for example, by several tenths of a degree. This heat can spread to an unirradiated neighboring element and there lead likewise to an output signal. The contrast of the sensor system is thus diminished. Moreover, it is thus far not possible to check the functional capability of the sensor system (including all individual sensor elements
10
) easily during operation.
The application of thermopiles to a carrier membrane which is a poor conductor of heat and is stretched over cavities etched in the carrier substrate is known from U.S. Pat. No. 3,801,949. The cavities serve for the thermal insulation of the sensor element
10
with regard to the substrate
15
and thus to increase the sensitivity of the sensor system. But cross talk is detected even with this design, so that the heat insulation of the individual sensor elements with respect to one another is not sufficient. Moreover, only a comparatively small part of the substrate surface is actually covered with sensor elements
10
, because the etched cavities, formed from the back side of the substrate, do not have vertical walls, which necessitates wide spacing between the individual sensor elements attached to the substrate. The detection sensitivity thus becomes too low, and relatively small point sources can become images on places between the sensor elements, as a result of image formation by the lens, so that they are not detected, and the sensor system will thus work unreliably.
FIG. 2
shows arrangements, in section as well as in the top view which is not to scale, as they are known in the state of the art. In
FIG. 2A
, the sensor element
10
is positioned over the etched cavity
24
, which has sloping walls. The sloping walls result due to the influence of the crystal orientation in the substrate
15
upon the known manufacturing process. The sensor elements
10
are thereby widely spaced from one another, so that the density with which the surface is filled is low and the detection reliability not satisfactory.
FIG. 2B
shows an embodiment where the etched cavities
25
have a rhomboid outline, with walls which are vertical in the direction of thickness. The rhomboid outline arises in the case of this embodiment likewise as a result of crystal orientation.
FIG. 2C
shows an embodiment, in which cavities
26
are formed by an etching process from the front side of the substrate. These cavities
26
also exhibit sloping walls
21
, so that the mutual spacing of the sensor elements
10
themselves is relatively wide.
FIG. 2D
, finally, shows an embodiment, in which a gap
23
is formed between the sensor element
10
and substrate
15
, by first applying a sacrificial layer and then removing it after formation of the sensor element
10
. Due to the small distance, the thermal insulation of the sensor element relative to the substrate
15
is poor, so that the signal amplitude and thus the sensitivity of the sensor system is low. Procedures based upon sacrificial layers are described, for example, in DE 19,539,696 A1 or in EP 0,534,768 or in PCT/EP89/01082. Processes making use of anisotropic etching behavior are described in EP 0,640,815 A1 or PCT/AU91/00162. In the case of the anisotropic etching process, the achievable packing density is restricted by the crystalline structure. The sacrificial-layer process results in high packing densities and low cross-talk levels. But because the tub or cavity depth is technologically limited to only a few &mgr;m, the thermal insulation of the sensor elements
10
and thus the signal amplitude are on the whole unsatisfactory.
BRIEF SUMMARY
Presented is a sensor system for the detection of thermal radiation, with a substrate (
15
) and several sensor elements (
10
) on the substrate (
15
), in which case at least one self-test device (
53
) is provided in order to generate heat which can be used for the heating of one or more sensor elements (
10
). The sensor elements (
10
) can be heated according to a typical time pattern during the self-testing process. Also presented is an advantageous process for the manufacture of the sensor system as well as an advantageous configuration of the total system, including signal processing.
Sensor system for the detection of thermal radiation, further is used with a substrate, several sensor elements, each attached to the substrate and each of which generates an electrical signal in proportion to the thermal radiation striking it. A signal-processing device converts at least the electrical output signals of sensor elements lying parallel to one another into a serial signal and delivers this to an output.
For monitoring by the sensor system during the self-testing process, the anticipated characteristic signal is extracted from the output signal of the sensor system on the basis of the operation of the self-test device, in order to serve as a signal for monitoring.
The goal of the invention is to create a sensor system which operates reliably and permits high quality signal detection.
A further task of the invention is to produce a sensor system whose operation can be easily monitored, as well as testing procedure for the same.
A further task of the invention is to create a sensor system which is small in size and cheap to produce.
These objections are achieved with the features in the independent claims. Dependent claims focus upon preferred embodiments of the invention.


REFERENCES:
patent: 3742231 (1973-06-01), Spielberger
patent: 3801949 (1974-04-01), Larrabee
patent: 5193911 (1993-03-01), Nix et al.
patent: 5753916 (1998-05-01), Ooisi et al.
patent: 195 39 696 A1 (1996-10-01), None
patent: 0 640 815 A1 (1995-03-01), None
patent: 0 534 768 B1 (1996-05-01), None
patent: WO 90/03560 (1990-04-01), None
patent: WO 91/166607 (1991-10-01), None

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