JP2001255206A - Thermal infrared photographing element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermal semiconductor infrared photographing element with high sensitivity. SOLUTION: A thermal infrared detecting element or a semiconductor p-n junction element whose temperature changes by absorbing infrared rays from a subject and whose resistance value changes with the temperature change, is characterized in that a direct-current component of a signal is passed through a constant current circuit 103 and the remainder component is led to an amplifying circuit 106.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a readout circuit for a thermal infrared imaging device which does not require a cooling device.

[0002]

2. Description of the Related Art In recent years, a bolometer type of vanadium oxide using a micromachining technology as a thermal infrared sensor that does not require a cooling device, or a BST (Barium-S
(Tronium-Titanium) has been commercialized. These products are composed of a heat-sensitive part that absorbs infrared rays to raise the temperature, support legs for thermally separating the heat-sensitive part from the silicon substrate, and X and Y address lines for selecting pixels. . In particular, vanadium oxide bolometer-type infrared imaging devices have been marketed in recent years because of their higher sensitivity than pyroelectric devices and simpler manufacturing methods. The bolometer-type sensor detects a change in resistance due to temperature, and generally expresses the material performance by a numerical value of a resistance change rate at a temperature change of 1 ° C. of a resistor called a temperature coefficient of resistance (TCR). However, the value is only about 2% for vanadium oxide and about 0.2% for titanium. In addition, the temperature rise of the heat-sensitive element portion with respect to an infrared input from the outside is at most about several mK. Therefore, several tenths of the current generated by the application of the bias voltage
Only a signal change of about 00% can be obtained. Therefore, most of the current was a DC component not related to the signal. The conventional readout circuit has a drawback that the noise caused by the current is increased and the sensitivity is deteriorated because all the bias current is input to the amplifier circuit.

[0003] In addition, a CCD (Charge Couple) is used.
In ed device, there is a phenomenon called "blooming" in which many optical signals are input to a certain pixel, and signal charges generated there leak out to an adjacent pixel. As a countermeasure against this, there is known a structure in which an overflow drain is provided to discard excess charges. However, this method discards the supernatant portion of the signal in principle, so that when applied to a thermal infrared imaging device, the signal portion is discarded. Therefore, it could not be applied to a thermal infrared imaging device.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a high-sensitivity thermal infrared imaging device.

[0005]

An infrared imaging device according to the present invention is capable of effectively shunting a current flowing through a thermosensitive element,
That is, the DC component is bypassed to the constant current circuit, and the remaining signal is led to the amplifier circuit.

[0006]

Embodiments of the present invention will be described below.

FIG. 1 is a view showing a part of a thermal infrared imaging device according to a first embodiment of the present invention. Each of the pixels 101 has a hollow structure formed for thermal isolation from a substrate and an active region in which a thermosensitive element whose resistance value changes according to temperature is formed. There are two supporting legs for mechanically supporting the substrate and the thermal element, and electrical wiring for guiding a signal generated by the thermal element to an electric processing circuit is formed in the supporting leg. A column is selected by the vertical scanning circuit 102,
A bias voltage is applied to all the pixels in the column, and the temperature of each pixel is distributed according to the irradiated infrared rays. Several meters for 1K of temperature difference of subject
A change of about K is expected. The current value flowing through the element is distributed according to the temperature change. However, the temperature coefficient of resistance A%
In the case of a thermosensitive element (generally A <10), at least (100−A × 0.001) / 100 of the total current is DC,
That is, it is a component that does not change due to an external temperature change. At most A × 0.001 / 100 is the signal portion. Therefore, approximately (100−A × 0.001) /
100 flows to the ground 104 through the constant current circuit 103, and only the remaining signal components of A × 0.001 / 100 pass through the current-voltage conversion circuit 105 and are input to the amplification circuit 106. The amplified signal can be directly supplied to the horizontal scanning circuit 107 or integrated for a predetermined time and output. In addition, the current-voltage conversion circuit may be directly converted using a resistor. However, noise can be further reduced by accumulating charges with a capacitor as shown in FIG. Although a resistor having a constant temperature coefficient of resistance has been described above as an example, the same applies to a sensing element which is forward-biased to a semiconductor pn junction whose current temperature coefficient (current change rate due to temperature) changes according to an applied voltage. The effect is obtained.

[0008]

As described above, according to the present invention, it is possible to manufacture a high-sensitivity thermal infrared imaging device which cannot be obtained by the conventional technology.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a conventional thermal infrared imaging device.

FIG. 3 is a diagram showing another embodiment of the present invention.

FIG. 4 is a diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 ... Pixel 102 ... Vertical scanning circuit 103 ... Constant current circuit 104 ... Ground 105 ... Current-voltage conversion circuit 106 ... Amplification circuit 107 ... Horizontal scanning circuit 108 ... Signal output 109 ... Vertical address line 110 ... Horizontal address line 201 ... Pixel 202 ... Vertical scanning circuit 203 Current / voltage conversion circuit 204 Amplifier circuit 205 Horizontal scanning circuit 206 Signal output 207 Vertical address line 208 Horizontal address line 301 Thermal resistor 302 Vertical scanning circuit 303 Constant current circuit 304 Ground 305: current-voltage conversion circuit 306: amplifier circuit 307: horizontal scanning circuit 308 ... signal output 309 ... vertical address line 310 ... horizontal address line 311 ... resistor 312 ... bypass current setting voltage 313 ... signal current shunt setting voltage 314 ... amplifier circuit power supply Voltage 315: constant current source 401 Diode 402 Vertical scanning circuit 403 Constant current circuit 404 Ground 405 Current voltage conversion circuit 406 Amplifier circuit 407 Horizontal scanning circuit 408 Signal output 409 Vertical address line 410 Horizontal address line 411 Resistance 412 Bypass current Set voltage 413 ... Signal current shunt setting voltage 414 ... Amplifier circuit power supply voltage 415 ... Constant current source 501 ... Diode 502 ... Vertical scan circuit 503 ... Constant current circuit 504 ... Ground 505 ... Current voltage converter 506 ... Amplifier circuit 507 ... Horizontal scan Circuit 508 Signal output 509 Vertical address line 510 Horizontal address line 511 Capacitor 512 Bypass current setting voltage 513 Signal current shunt setting voltage 514 Amplifier circuit power supply voltage 515 Constant current source 516 Reset signal 517 Reading timing Faith 518 ... reset voltage

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G01J 5/48 G01J 5/48 A H01L 27/14 H04N 5/33 H04N 5/33 H01L 27/14 K F term (reference) 2G065 AA04 AA11 AB02 BA12 BA14 BA34 BA40 BC01 CA30 DA18 2G066 BA09 BA60 BB20 CA02 4M118 AA05 AB01 BA03 CA03 CA14 CA16 DD08 FA06 FA33 HA22 HA40 5C024 AX06 CX03 HX02 HX17 HX48

Claims (3)

[Claims] 1. A current flowing through a constant current circuit and a path flowing through an amplifier circuit among currents modulated by a temperature change of a thermosensitive element section, and only a signal flowing through the amplifier circuit is amplified and output. Thermal infrared imaging device. 2. The thermal infrared imaging device according to claim 1, wherein a pn junction is used as the thermal element. 3. The thermal infrared imaging device according to claim 1, wherein an element for biasing a pn junction in a forward direction is used as the thermal element.