Semiconductor memory device

Details Semiconductor memory device Semiconductor memory device

1999-10-06

2002-03-19

Nguyen, Vinh P. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

76

Reexamination Certificate

active

06359460

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor device, and more particularly to a semiconductor device provided with an integration circuit comprising a resistance and a capacitor accumulating currents flowing through them for detecting variation in resistance value of the resistances in order to detect variation in various physical value (such as infrared ray, microwave/milliwave, temperature, magnetic, and pressure) such as an infrared ray sensor, a microwave/milliwave detector, a temperature sensor, a magnetic sensor, a pressure sensor, a gas sensor and a flow sensor.
The description will hereinafter be made by an example of focusing a thermal infrared ray image pick-up device. Notwithstanding this example, the present invention is applicable to all semiconductor devices that integrate faint signal components for detection.
DESCRIPTION OF THE RELATED ART
A conventional thermal infrared ray image pick-up device is mentioned in Japanese laid-open patent publication No. 9-315455.
FIG. 14
is a cross sectional view illustrative of the conventional thermal infrared ray image pick-up device mentioned in Japanese laid-open patent publication No. 9-315455.
As illustrated in this drawing, a semiconductor substrate
1401
is formed with a scanning circuit
1402
over which a plurality of photo-receiving regions
1400
for converting an incident infrared ray into electric signals.
One of the photo-receiving regions
1400
comprises a single pixel of the image pick-up device. In order to obtain a two-dimensional infrared ray image, a two-dimensional integration of plural pixels. Under the photo-receiving regions
1400
, there is a two-dimensional integration of scanning circuits
1402
for reading out image data picked up.
The photo-receiving region
1400
has a film-structure so called as a diaphragm. In a diaphragm
1403
in the drawing, a cavity
1404
is formed at its bottom portion. This cavity
1404
is formed by removing a previously formed dummy layer, via an etching process.
On a surface of the diaphragm
1403
, an infrared ray absorption layer
1405
is formed for absorbing the infrared ray. At a boundary between the diaphragm
1403
and the cavity
1404
, a thermoelectric converter
1406
is formed for converting a heat generated due to receipt of the infrared ray into an electric signal. As this thermoelectric converter
1406
, a bolometer is used in this example that varies in electric resistance depending upon temperature. Titanium is, for example, used for the bolometer.
Meanwhile, operations of the thermal infrared ray image pick-up device of
FIG. 14
will briefly be described as follows.
An incident infrared ray into the photo-receiving region
1400
in each pixel is absorbed into the infrared ray absorption layer
1405
to cause an increase in temperature of the diaphragm
1403
in each pixel, whereby this temperature increase is converted by the thermoelectric converter
1406
(bolometer) into electric signals which are then read-out sequentially via the scanning circuit.
The thermal infrared ray image pick-up device of
FIG. 14
will be described in detail.
FIG. 15
shows a read-out circuit used in the thermal infrared ray image pick-up device of FIG.
14
.
As shown in the drawing, a read-out circuit
1500
is provided with a plurality of bolometer
1501
, pixel switches
1509
connected between the bolometers
1501
and a ground, an NPN transistor
1502
, a cancel resistance
1503
, a PNP transistor
1504
, an integration capacitor
1505
, a sample hold circuit
1506
, an FPN correction constant current source
1507
, and a reset switch
1508
opening/closing upon an input of a reset signal &PHgr;R.
The sample hold circuit
1506
comprises NMOS transistors
1510
and
1511
on a former stage, a switch
1512
opening/closing in accordance with an externally inputted sample hold pulse &PHgr;S/H, a hold capacitor
1513
and NMOS transistors
1514
and
1515
on a later stage.
As described in
FIG. 14
, the bolometer
1501
senses a heat generation due to an incident infrared ray for conversion into electric signals. For example, if a voltage Vb
1
is applied to a base of the NPN transistor
1502
, the bolometer
1501
is applied with a voltage Vb
1
−VBE where VBE is a base-emitter voltage. A collector of the NPN transistor
1502
is applied with a current Ic
1
=(Vb
1
−VBE)/Rb
1
where Rb
1
is a resistance of the bolometer.
If a voltage Vb
2
is applied to a base of the PNP transistor
1504
, a collector of the NPN transistor
1504
is applied with a current Ic
2
=(Vb
2
−VBE)/Rb
2
where Rb
2
is a resistance of the cancel resistance.
Ic
1
and Ic
2
are almost balanced with each other but are slightly different from each other, for which reason the integration capacitor
1505
is applied with a slight difference &Dgr;I=Ic
1
−Ic
2
. Namely, this difference &Dgr;I is a sum of a signal component and a remaining bias component, wherein a majority of the bias component has been removed.
The externally incident infrared ray causes a temperature increase of the diaphragm
1403
thermally isolated (
FIG. 14
) to cause variation in resistance value of the bolometer
1501
. This variation in resistance value causes a variation of Ic
1
, whereby the difference &Dgr;I is accumulated in the integration capacitor
1505
.
The bias component, which could not be removed, is caused by variation of the plural bolometers
1501
sequentially selected in the most case. Since the single cancel resistance
1503
is used, Rb
2
is fixed. Since, however, the plural bolometers
1501
are used, if there is a large variation in Rb
2
of majority of them, there is also variation in the difference &Dgr;I.
In order to correct the variation, in prior art, the FPN correction constant current source
1507
is further provided.
This FPN correction constant current circuit
1507
comprises plural-staged constant current sources not illustrated. Each of the constant current sources has a current value which is weighted with an integer power of 2, such as I
0
, 2·I
0
, 4·I
0
, . . . In accordance with variation of Rb
1
, a desirable one is selected form the constant current sources in order to reduce variation in the difference &Dgr;I due to the variation of Rb
1
.
The corrected signal is accumulated in the integration capacitor
1505
and then converted from a high impedance to a low impedance by a source-follower in the sample hold circuit
1506
. Time-sequentially sampled signals are temporary held in the hold capacitor
1513
and then outputted as outputs S/Hout. This output S/Hout is read out by the scanning circuit
1402
, shown in FIG.
14
.
The conventional thermal infrared ray image pick-up device has an issue of how to improve the temperature characteristics of the integration circuit comprising the integration capacitor
1505
. The following has already been proposed as a circuit for improving the temperature characteristic of the integration circuit.
As shown in Japanese laid-open patent publication No. 2-260914, an integration circuit comprising a capacitor and a diffusion resistance is added with another diffusion resistance for compensation to a temperature dependency of a leakage of current through the diffusion resistance, so that the leakage of current is accumulated to the capacitor.
In Japanese laid-open patent publication No. 3-103711, it is mentioned that in order to prevent variation in output voltage from a magnetic sensor over temperature, the constant current source varies a current value depending upon temperature.
In Japanese laid-open patent publication No. 8-320266, it is mentioned that a constant current source having a constant current characteristic with a zero temperature coefficient is used to fix a current flowing through a piezo-resistance independently from temperature.
In Japanese laid-open patent publication No. 8-334413, it is mentioned that further to bolometers of the individual pixels, a temperature compensation resistance is provided which has the same material and structure as the bol

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