JP3217533B2 - Infrared sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared sensor for detecting infrared rays emitted from an object, and more particularly to an infrared sensor capable of accurately detecting whether an object is stopped or moving with a single element. It is about.

[0002]

2. Description of the Related Art A thermopile or pyroelectric element using a thermocouple is typically used as an element for generating heat by receiving infrared rays emitted from an object and converting the heat into an electric signal to detect the infrared rays. There is a pyroelectric element using the body. These are used in a wide variety of applications, such as home appliances, medical equipment, control units of various furnaces, security equipment, fire alarms, and automatic number measurement, which take advantage of their characteristics to detect heat sources.

FIG . 6 shows a basic structure of a thermopile. An insulating thin film 2 is formed on the surface of a semiconductor substrate 1, and a different type of metal or semiconductors 3 and 4 are bonded and arranged on the insulating thin film 2 to form a thermocouple. The semiconductor substrate layer below the region is removed. In the thermopile, when infrared rays are incident and the joint is heated, an electromotive force is generated between the dissimilar metals or semiconductors 3 and 4 by the Seebeck effect, and the infrared rays are detected by the electromotive force.
Usually, the thermopile used is such that a plurality of thermocouples having the above structure are connected in series to obtain a sufficient voltage. The advantage of the thermopile is that the temperature can be measured in a non-contact state by providing a separate processing circuit, and it can be detected with high sensitivity in a steady state where the incident infrared ray does not change with time. . However, a disadvantage is that it is relatively insensitive to infrared light that changes over time.

FIG . 7 shows a basic structure of a pyroelectric element. An insulating thin film 6 is formed on the surface of a semiconductor substrate 5, and a lower electrode 7, a pyroelectric thin film 8, and an upper electrode 9 are disposed on the insulating thin film 6 in a laminated structure. The semiconductor substrate layer below the central region is removed. In the pyroelectric element,
When infrared light is incident and the pyroelectric thin film 8 is heated, charges are induced in the upper electrode 9 and the lower electrode 7 by the pyroelectric effect,
An electromotive force is generated. Infrared rays are detected by this electromotive force. The advantage of the pyroelectric element is that it has the ability to detect with high sensitivity when the incident infrared ray changes over time, and that by arranging a plurality of pyroelectric elements thereon, it is possible to detect the moving direction of the object. . On the other hand, a disadvantage is that due to the characteristics of the pyroelectric effect, a high-sensitivity output can be obtained when the incident infrared ray changes with time, but the output becomes zero when the incident infrared ray is in a steady state. Therefore, when a stationary infrared ray from a stationary object is detected by the pyroelectric element, a special operation such as chopping the infrared ray is required. Since the thermopile and pyroelectric element each have the above-mentioned disadvantages, conventionally, when detecting infrared light from a moving object and infrared light from a stationary object without fail, conventionally, the thermopile and the pyroelectric element are used. A method in which both elements are used in combination has been adopted.

[0005]

Conventionally, a thermopile and a pyroelectric element are separate elements, and when a thermopile and a pyroelectric element are used together, it is, of course, necessary to individually incorporate them into a handling device or the like. There is a problem in that the space is individually occupied in terms of the target and the electric circuit, which requires a large space and increases the cost. The present invention has been made to solve the above problems,
An object of the present invention is to provide an infrared sensor in which a single element has both functions of a thermopile and a pyroelectric element.

[0006]

According to the infrared sensor of the present invention, a pyroelectric element portion and a thermopile portion are integrally formed in a laminated structure on the same upper insulating thin film formed on the surface of a semiconductor substrate, and the thermopile and the thermopile are integrated. It has both functions of the electric element.

[0007]

With the above arrangement, infrared rays emitted from a stationary object are detected by the thermopile unit, and infrared rays emitted from a moving object are detected by the pyroelectric element unit. , It is possible to accurately detect both moving and stationary objects.

[0008]

1A and 1B show an embodiment of the present invention. 1A is a plan view, FIG. 1B is a cross-sectional view taken along the line AA in FIG. 1A, 10 is a semiconductor substrate of an n-type Si crystal piece, 11 is a top insulating thin film made of SiO ₂ , 12
Denotes a contact area between the semiconductor substrate 10 and the upper insulating thin film 11;
Is a cavity region, 14 is a lower electrode formed of Pt, and 15 is Pb.
TiO ₃ , Pb (Zr, Ti) O ₃ , (Pb, La) (Z
a pyroelectric thin film 16 made of (r, Ti) O ₃ or the like; 16 is an upper electrode formed of Au; the lower electrode 14 and the pyroelectric thin film 15
And the upper electrode 16 constitute a pyroelectric element portion. 29 is above
SiO ₂ film formed by a CVD method so as to cover the unit electrodes 16
And 19 is (BiSb) ₂ T
thermoelectric material A having a positive thermoelectric power such as e ₃ , PbTe, ZnSb, etc., 20 is Bi ₂ (TeSe) ₃ , InSb, I
A thermoelectric material B having a negative thermoelectric power such as nAsP, and these different thermoelectric materials A and B are alternately connected in series and arranged to form a plurality of thermocouples. The thermocouple forms the thermopile. In FIG. 1A, the heat is hidden by the absorber 27,
For the hot junction of the electronic materials A, Otsu 19 and 20, the upper insulating thin film 29
The cold junction 18 is formed on the contact area 12 of the upper surface insulating thin film 11 in a non-contact structure on the pyroelectric element portion via the intermediary . Reference numerals 22 and 23 denote thermoelectric material shells of the thermopile portion, electrode pads electrically connected to ends 19 and 20, respectively.
5 is an electrode pad electrically connected to the electrodes 14 and 16 of the pyroelectric element portion, 26 is a metal frame holding the semiconductor substrate 10, 27 is an absorber for absorbing infrared rays,
The O ₂ film is coated with Au black or Bi black. 28
Is a lower surface insulating thin film.

The manufacturing method of the embodiment shown in FIG .
An SiO ₂ film is formed on both upper and lower surfaces of a single semiconductor substrate 10 made of crystal pieces by thermal oxidation, and an upper insulating thin film 11 and a lower insulating thin film 28 are provided on both upper and lower surfaces, respectively . Then , the central portion of the lower insulating film 28 is removed by etching .
You. Next , Pt is formed on the upper insulating thin film 11 by sputtering.
Is deposited to form a lower electrode 14, on which PbTiO ₃ , Pb (Zr, T
i) O ₃ (Pb, La) (Zr, Ti) O ₃ or the like is deposited to form a pyroelectric thin film 15, and Au is deposited thereon by vapor deposition to form an upper electrode 16. As described above, the lower electrode 14 formed on the laminated structure, the pyroelectric thin film 15, and constitute the pyroelectric element portion in the upper electrode 16, the shape of each of Patent
The shape need not be limited to a square, but may be a circle, a rectangle, or a polygon. The selective etching of the lower electrode 14 on which Pt is deposited is performed by a reverse sputtering method using PbTiO ₃ , Pb (Zr, T
i) For selective etching of the pyroelectric thin film 15 on which O ₃ , (Pb, La) (Zr, Ti) O ₃ or the like is deposited, a mixed diluent of HF and HCl is used. Aqua regia or oxytron may be used for the selective etching.

Next, at least cover the pyroelectric element portion.
Form upper insulating thin film 29 made of SiO ₂ film by CVD method
I do. Then, a thermoelectric material layer 19 and a thermoelectric material layer 20 are arranged on the upper insulating thin film 11 and the upper insulating thin film 29 to form a plurality of thermocouples constituting a thermopile portion. , 20 in a predetermined shape, a photoresist is previously deposited as a dummy at a place other than the place where the thermoelectric material is placed, and after the material is deposited from one direction, a necessary place together with the photoresist is deposited. The lift-off method for removing other materials may be repeated. Absorber 27 includes upper insulating thin film 29 on upper electrode 16.
Alternatively, the thermoelectric material can be used to form SiO on CVD
₂ film is deposited, and Au, Bi, etc. are deposited thereon in an N ₂ atmosphere, and unnecessary portions are removed by a lift-off method.
I do. Next, using the lower surface insulating thin film 28 formed on the lower surface of the semiconductor substrate 10 by thermal oxidation and removing the central region by etching as a mask, the semiconductor substrate layer 10 is etched with an n-type Si etchant such as an alkaline etchant of NaOH or KOH or an aqueous solution of hydrazine. Is etched. The etching stop time is appropriately controlled, and etching is performed until the etching reaches the lower surface of the upper insulating thin film 11 to form a cavity region 13 . In addition ,
The plane orientation of the n-type Si crystal piece of the semiconductor substrate 10 is (100)
When selective etching is performed using a mask obtained by etching the central part of the lower insulating thin film 28 on the surface or the (110) surface, the direction of the rectangular side is changed to <110> or <21>.
By conforming to <1>, more precise processing can be performed.

An object moves in front of the element having such a configuration.
When moving or stopped, the infrared light emitted from the object is light
The light enters the upper part of the cavity 13 through the academic system. And infrared
The wire turns into heat at that point. At this time, the upper part of the cavity area 13
Has high thermal resistance and high temperature
You. And since the thermal resistance is small at the upper part of the contact area 12,
For example, even if heat is conducted from the upper part of the cavity region 13,
The temperature is kept at the same level as the room temperature. Therefore, cavity area 1
3 near the upper electrode 16 of the pyroelectric element portion formed above
Next to and directly below the pyroelectric thin film 15 and the pyroelectric element section
The temperature in the vicinity of the hot junction 17 of the mopile portion increases. Change
In addition, due to the effect of the absorber 27 appropriately provided,
Temperature is obtained. Here, the incident infrared rays
If it is a steady one, the hot junction and the cold
A steady temperature difference occurs between the contacts 18 and the
A thermoelectromotive force is obtained. Note that a plurality of heat
If the thermocouple is connected in series, the electrode pads 22, 23
Thus, a detection signal increased several times is obtained. Furthermore, the radiation of the object
Take a method of processing in an external circuit taking into account the firing distance
For example, the temperature of an object can be measured without contact. object
Is moving and the emitted infrared light changes over time
In this case, the upper electrode 16 and the lower electrode
Electric charges are induced by the pyroelectric effect of the pyroelectric thin film 15 in between,
Detection signals are obtained from the electrode pads 24 and 25.

When the object is stationary as described above,
If the infrared radiation is steady,
High detection signal is obtained, the object is moving,
If the infrared light changes with time, the pyroelectric element
, A highly sensitive detection signal is obtained. That is, a single
Element detects with high sensitivity even when the object is stopped
can do.

The shapes of the pyroelectric element and thermopile are limited
However, as shown in FIG.
Covers the entire surface of the upper insulating thin film 11 and the pyroelectric thin film 15
The electrode 14 may have a shape that covers the entire surface of the unit electrode 14.
The film 29 covers the entire surface of the upper electrode 16 and the pyroelectric thin film 15
Shape may be sufficient. These shapes are required for infrared detection
It can be selected flexibly according to the balance between characteristics and manufacturing cost. sand
That is, as described above, the infrared ray emitted from the object is in the cavity area 1
3 and is converted into heat at the upper part of the contact area 3 and the contact area 12
The thinner the pyroelectric thin film 15, the upper insulating thin film 29, and the like are,
Low heat capacity, high heat resistance, high detection sensitivity
Become. It is a photo-etching process that is performed many times.
This can be achieved by selectively processing the thin film.
High. These thin films are selectively processed.
It is cheaper to cover the entire surface. Above
For this reason, the lower electrode 14, the pyroelectric thin film 15, the upper electrode
The shape of 16 does not need to be limited,
What is necessary is just to make it a suitable shape. The structure of the cavity 13 is
It is the same as above.

FIGS. 3A and 3B show two elements in one element.
An example in which a pyroelectric element portion is provided will be described. FIG. 3A is a plan view.
FIG. 3B is a cross-sectional view taken along the line BB of FIG. 3A.
It is. In the region above the cavity region 13 of the upper surface insulating thin film 11
Rectangular lower electrode 14a, pyroelectric thin film 15a, upper electrode
14b having the same shape as the first pyroelectric element portion made of 16a,
A second pyroelectric element portion composed of 15b and 16b;
The detection signals from the second pyroelectric elements are respectively applied to the electrode pads 2.
4a, 25a and 24b, 25b.
ing. In this embodiment, the radiation from a moving object is
When the infrared ray moves from right to left, the electrode pad 2
4a, 25a previously appears detection signal, and the electrode after mow
A detection signal appears on the pads 24b and 25b. Incident infrared
When the line moves from left to right, the electrode pad 24b,
25b, a detection signal appears first, and then an electrode pad
Detection signals appear at 24a and 25a. Therefore, the first
Whether the detection signal from the pyroelectric element section is earlier in time or the second pyroelectric element
By identifying whether the detection signal from the element section is first,
The direction of movement of the body can be detected.

Next, examples of the detection signal of each embodiment will be described. Transfer
This is a case where the speed of the moving object is 10 m / s. FIG.
(A) and (b) show the temperatures of a plurality of thermocouples for comparison with the present invention.
The contact 17 is between the upper electrode 16 of the pyroelectric element portion and the contact area 12.
It is formed between them. In the structure shown in FIG.
1.2 × 10 ⁴ V from the pyroelectric element when moving left and right
/ W detection signal indicates that the object is stationary
The detection signal was 5.5 × 10 ² V / W from the
On the other hand, in the embodiment shown in FIG.
The detection signal of 5.0 × 10 ³ V / W from the element stops the object.
9.6 × 10 ² V /
A detection signal of W was obtained. In the embodiment shown in FIG.
Moves from right to left, as shown in FIG.
The detection signal from the first pyroelectric element section is
If the object moves in the opposite direction, obtained before the detection signal
Detection from the first pyroelectric element as shown in FIG.
Signal is obtained prior to the detection signal from the second pyroelectric element section.
Thus, it was possible to detect the moving direction of the object. Also, if the object
When stopped, 9 × 10 ³ V /
A detection signal of W was obtained.

[0016]

As described above, according to the present invention, simply
From an object stopped at one element and a moving object
Can be detected with high sensitivity.
The storage space can be small, and if the cost is low
This has the effect. In addition, the thermoelectric material
Is arranged in a non-contact structure with the pyroelectric element, and the hot junction is
By forming it on the center part as much as possible,
The detection signal with higher sensitivity can be obtained from the file part.

[Brief description of the drawings]

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

FIG. 2 is a view showing an embodiment in which the shape of a pyroelectric element portion is different.
You.

FIG. 3 is a diagram showing another embodiment having two pyroelectric elements.
is there.

FIG. 4 shows a structure of an infrared sensor comparing detection signals .
FIG.

5 is an infrared ray from a moving object according to another embodiment shown in FIG . 3;
FIG. 7 is a diagram showing an example of the detection signal of FIG.

FIG. 6 is a diagram showing a basic structure of a thermopile.

FIG. 7 is a diagram showing a basic structure of a pyroelectric element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Semiconductor substrate 11 Upper surface insulating thin film 12 Adhesion area 13 Cavity area 14 Lower electrode 15 Pyroelectric thin film 16 Upper electrode 17 Hot junction 18 Cold junction 19 Thermoelectric material A 20 Thermoelectric material O 22, 23 Electrode pad 24, 25 Electrode pad 26 Metal frame 27 Absorber 28 Bottom insulating thin film

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 37/02 G01J 5/02 H01L 35/32

Claims (1)

(57) [Claims] 1. A lower portion disposed in a laminated structure on an upper surface insulating thin film having a cavity region formed by removing a semiconductor substrate layer below a central portion region formed on a surface of a semiconductor substrate and surrounded by a peripheral portion thereof. consisting of electrodes and the pyroelectric thin film and the upper electrode and the pyroelectric element portion, double
The thermopile section consisting of a number of thermocouples and the upper insulating thin film
Disposed in a laminated structure through the hot junction of the thermopile section
Is the area corresponding to the cavity area,
The contacts are located in the area corresponding to the peripheral semiconductor substrate layer.
An infrared sensor characterized by being placed .