JPH0794693A - Semiconductor infrared image sensing element - Google Patents

Abstract

PURPOSE:To provide a structure of an infrared detection element which can detect a good image at a room temperature or thereabout by subjecting exter nally incoming infrared ray to optical modulation in order to separate the charges generated thereby from the charges generated based on the temperature of a semiconductor element and then picking up only the electrically modulated component. CONSTITUTION:An insulator 11 and a resistor 10 are formed between a diode having a light receiving layer comprising HgCdTe layers 5, 6 formed oppositely to a silicon charge transfer element 1 and the junction thereof, i.e., an indium bonded column 4. A part for optically modulating the incident infrared ray is also provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor infrared image pickup device.

[0002]

2. Description of the Related Art In principle, infrared detectors can be classified into quantum detectors using semiconductors and pyroelectric detectors utilizing the pyroelectric effect. When the conventional quantum detector is used for the purpose of detecting radiation near room temperature when the element temperature is around room temperature, the band gap of the detector material is about 0.12 eV.
Since it is small, the electric charge generated by the heat of the detector itself becomes noise and it is not possible to separate the infrared rays from the subject, so a clear image could not be obtained except for the detectors for strong infrared rays such as carbon dioxide gas laser. . Therefore, most quantum detectors cannot detect infrared rays with high sensitivity unless they are equipped with a cooling system such as a Joule-Thomson type or a Stirling cycle type refrigerator and cooled to liquid nitrogen temperature (absolute temperature 77 degrees). . Therefore, the imaging system has become large-scale, and the application of the infrared imaging camera has been limited to defense and space equipment.

On the other hand, although the pyroelectric detector detects infrared rays at room temperature, it is in principle a detector for detecting the temperature rise of the element, and therefore has a lower sensitivity and a faster response speed than the quantum detector using a semiconductor. It is not used as an image sensor because it is slow.

As a conventional infrared detector, JMArias et al.
(Appl. Phys. Lett. 62 (1993) 976) suggested by the structure shown in FIG. This infrared detector is composed of a Si charge transfer device wafer 1 having a charge injection electrode 12 formed on the surface thereof and an n-type HgC film on a CdZnTe substrate 3.
The dTe layer 5, the HgCdTe layer 7, and the CdTe layer 8 are sequentially formed, and the p-type HgCdTe layer 6 is formed on the HgCdTe layer 7.
It was formed by connecting the infrared light receiving portion formed with the gold electrode 9 and the In metal pillar 4. This allows p-type HgCdT
Since the p ⁺ layer of the e layer 6 has a wide bandgap and can exist as a p-type layer even at about 300 K, it was expected as an infrared detector operating near room temperature.

However, although the pn junction is present, the charge generated by the heat of the detector itself is large, so that it exceeds the charge capacity of the charge transfer element 1 in the figure, and the temperature at which an infrared image can be obtained is still high. It was the same as liquid nitrogen temperature without thermal noise.

[0006]

The conventional infrared image pickup device cannot obtain an infrared image having high sensitivity at a temperature that can be cooled by an electronic cooler using the Peltier effect. The present invention provides a semiconductor infrared imaging device which has high sensitivity not only at low temperatures but also near room temperature.

[0007]

SUMMARY OF THE INVENTION The present invention is a semiconductor infrared imaging device having a light receiving section for receiving infrared rays and converting them into electric charges, and a charge transfer section for outputting the electric charges as an image signal. The AC component due to the incident electric charge is injected into the charge transfer unit through a capacitor, and the DC component due to the electric charge generated as thermal noise in the light receiving unit is discharged to a low potential before being injected into the charge transfer unit. The present invention provides a semiconductor infrared imaging device.

In particular, the charge obtained by photoelectrically converting the incident light, which has been optically modulated, within a time of 1/2 or less, preferably 1/10 or less of the charge accumulation time of the charge transfer portion is stored in the light receiving portion itself. It is preferable to separate the charge generated by heat and inject it into the charge transfer portion.

Further, the photoelectric conversion portion of the light receiving portion is set to HgCd.
In addition to Te, it is preferable to use CdTe as an insulator material for the resistor and the capacitor that removes the DC component from the ground.

[0010]

According to the present invention, the signal sent from the light receiving section to the charge transfer section is separated into an AC component which is an image signal and a DC component which is thermal noise, and the DC component is grounded.
The sensitivity can be improved even near room temperature.

[0011]

EXAMPLES The details of the present invention will be described below with reference to examples. The first embodiment of the present invention is shown in FIG. First, Cd
Metallic mercury (Hg), dimethyl cadmium on ZnTe substrate 3
N-type Hg _0.62 Cd _0.16 Te by metalorganic chemical vapor deposition using (DMCd) and diisopropyl tellurium (DIPTe) as raw materials.
Layer 5 is about 10 μm, arsenic added p-type Hg _0.66 Cd _0.34 Te
Layer 6 was grown continuously to 1 μm. Trimethylarsenic was used as the arsenic raw material and the supply rate was 5 × 10 ^-5 mol / min. A 64 × 64 mesa type diode array having a junction area of 30 × 30 μm ² and an element interval of 50 μm was produced from this growth layer by using a photolithography technique. A high resistance i-type CdTe layer 8 and an arsenic-added p-type CdTe layer 10 were successively grown on the diode array by metal organic chemical vapor deposition in a thickness of 0.3 μm and 0.2 μm, respectively. Trimethylarsenic was used for arsenic addition and the supply amount was 2.5.
× 10 ^-5 mol / min. The growth temperature is 3 when the HgCdTe layer is grown.
80 ° C., 320 ° C. during CdTe growth.

Furthermore, after the CdTe layers 8 and 10 to diameter 15μm removed covering the bonding electrode part by the photolithography technique, and 0.4μm depositing gold electrodes 9 ₁ to moieties its removal, the thickness for a further entire surface The undoped high resistance i-type CdTe layer 11 having a thickness of 0.1 μm was laminated as an insulator, and finally the gold electrode 9 ₂ having a diameter of 30 μm and a thickness of 0.5 μm was laminated to complete the photoelectric conversion section 100.

After that, a Si MOS switch array (which was used for infrared detectors in the past)
1), the indium pillar 4 having a thickness of 20 μm and a height of 20 μm is erected on the electrode 12 of the charge transfer unit 200, and the photoelectric conversion unit 100 is pressed to complete the two-dimensional infrared imaging device. It was Ga instead of indium pillar 4
Pillars or gold electrodes may be used. Reference numeral 14 is a ground electrode formed on the surface of the MOS switch array, and the p-type CdTe layer 10 was connected to this electrode through the column 4 of indium. Although it is connected to the ground electrode here, it is more preferable that the potential is lower than the direct current component that causes thermal noise, preferably a constant potential, for example, a negative power supply potential supplied to the MOS switch array.

FIG. 2 shows the connection state of the photoelectric conversion unit 100 and the charge transfer unit 200 by an equivalent circuit. Gold electrode 9
_An undoped high resistance i-type CdTe layer 11 serving as an insulating film of a capacitor is arranged between ₁ and 9 ₂ , and charges are injected into the charge transfer unit 200 via this capacitor as an AC component. Reference numeral 22 denotes injected charges, and 21 denotes an output terminal of the charge transfer unit 200. Here, the relationship between the modulation time of the incident light and the accumulation time of the charge 22 of the charge transfer unit 200 is determined so that the injected charge 22 can be output before it overflows. Therefore, the charge transfer unit 200
The charge obtained by photoelectrically converting the incident light, which is optically modulated in a time of 1/2 or less, preferably 1/10 or less, is separated from the charge generated by the heat of the light receiving portion itself. Then, it is injected into the charge transfer section. 1 / in the first embodiment
It was set to 10. Further, the p-type CdTe layer 10 functions as a high resistance element, and the direct current component is discharged and removed through the ground electrode of the CCD with the MOS switch array. As a result, thermal noise can be reliably removed.

As shown in FIG. 3, the infrared imaging element 16 is grounded on the base body 19 and is cooled by the electronic cooler 19 using the Peltier effect while passing through the 300 Hz chopper 14 provided outside the optical lens 15. The infrared light image 13 was taken. Reference numeral 20 is an electronic cooling control device. The image signal obtained from the infrared imaging device 16 is used as the image processing device 17.
And imaged by the display device 18. In this way, an infrared imaging system using the infrared imaging element 16 was constructed.

Although the image was slightly lacking in contrast at room temperature, a good image was obtained when the temperature of the element 16 fell below 0 ° C., and the sensitivity (NETD: noise equivalent temperature difference) was 0.1 K.
And, the same thing as the conventional liquid nitrogen temperature cooling type HgCdTe infrared detector was obtained.

Next, a second embodiment will be described with reference to FIG. As shown in FIG. 4, in this embodiment, as in the first embodiment, Hg _0.62 Cd _0.16 was formed on the CdZnTe substrate 3 by metal organic chemical vapor deposition using metallic mercury, dimethylcadmium, diisopropyl tellurium and trimethylarsenic as raw materials. T
e layer 5 of about 10 μm, undoped n-type Hg _0.66 Cd _0.34
The Te layer 7 was continuously grown to 1 μm, the CdTe layer 8 was grown to 0.3 μm, and the arsenic-added CdTe layer 10 was grown to 0.2 μm.
By removing the two layers of the dTe layer and the CdTe layer, arsenic is ion-implanted into the region having a diameter of 30 μm including the removed region with 350 keV and a dose amount of 1 × 10 ¹⁴ cm ^-2 to form the p-type region 6. , P-n junction was formed. The growth conditions are the same as in the first embodiment.

Then, a gold electrode of 0.4 μm is formed on the removed portion.
m vapor-deposited over the entire wafer, thickness of 0.1 μm
Layered insulators, and finally diameter 30μm thickness 0.5μm
Of gold electrodes were laminated.

Further, an indium pillar 4 having a thickness of 20 μm and a height of 20 μm is erected on the electrode 12 of the charge injection portion of the Si MOS switch array (with the latter stage CCD) used for the infrared detector, and then the diode is formed. and electrodes 9 ₂ and pressure of the array to produce a two-dimensional infrared detectors. Similar to the first embodiment, as shown in FIG. 3, the detector is cooled by an electronic cooler using the Peltier effect, and an image of infrared light is transmitted through a 300 Hz chopper provided outside the optical lens. I took a picture. Although the image was slightly lacking in contrast at room temperature, a good image was obtained when the element temperature fell below 0 ° C, and the sensitivity (NETD) was 0.1K, which is equivalent to that of the conventional liquid nitrogen temperature-cooled HgCdTe infrared detector. Things have been obtained.

As the insulator layer of the capacitor, the CdTe layer is used in the above-mentioned embodiment, but a II-IV group compound semiconductor other than this which becomes a high resistance layer, for example, undoped i-type ZnS is also similarly preferable. An image was obtained.

Further, instead of the mechanical chopper provided outside the optical lens 15, the CdZnTe of the above embodiment is used.
It is also possible to newly stack AgGaS ₂ or AgGaSe ₂ on the back surface of the substrate and generate an electric field by energizing this layer to change the transmittance of infrared rays. In this case, there is an advantage that the entire infrared imaging system becomes compact. In addition to having a good image at -5 ℃ or less, sensitivity (NET
D) is 0.1K and is the conventional liquid nitrogen temperature cooling type HgCdT
e The same thing as the infrared detector was obtained.

The charge transfer section need not be provided with a Si MOS switch array CCD, but may be a simple CCD without this switch or a stack type CCD. The present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0023]

As described above, according to the present invention, it becomes possible to fabricate an infrared detecting element sensitive to infrared rays near room temperature, which has not been obtained by the prior art.

[Brief description of drawings]

FIG. 1 is a sectional view showing a semiconductor photoelectric conversion element obtained according to a first embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of a semiconductor photoelectric conversion device obtained according to the first embodiment of the present invention.

FIG. 3 is a system diagram of a semiconductor photoelectric conversion device obtained according to the first embodiment of the present invention.

FIG. 4 is a sectional view showing a semiconductor photoelectric conversion device obtained according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a conventional infrared light receiving element.

[Explanation of symbols]

1 ... Charge transfer part of silicon 2 ... P-type HgCdTe layer 3 ... CdZnTe substrate 4 ... Indium metal pillar 5 ... n-type Hg _0.62 Cd _0.16 Te layer 6 ... Arsenic-added p-type Hg _0.66 Cd _0.34 Te layer 7 ... Hg _0.66 Cd _0.34 Te layer 8 ... CdTe layer 9 ... Gold electrode 10 ... Resistor layer (arsenic-added CdTe) 11 ... Insulator layer (CdTe) 12 ... Charge injection electrode 13 ... Subject 14 ... Optical chopper 15 ... Optical system 16 ... Infrared detector 17 … Drive circuit 18… TV monitor 19… Electronic cooler 20… Electronic cooling controller

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Katsuyoshi Fukuda No. 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Incorporated Toshiba Research and Development Center

Claims (1)

[Claims] 1. A semiconductor infrared imaging device having a light receiving section for receiving infrared rays and converting the infrared rays into electric charges, and a charge transfer section for outputting the electric charges as an image signal. A semiconductor infrared imaging device characterized in that a component is injected into the charge transfer unit through a capacitor, and a direct current component due to a charge generated as thermal noise in the light receiving unit is released and removed to a low potential before being injected into the charge transfer unit. element.