JP2787198B2 - Thin film pyroelectric infrared detecting element and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin-film pyroelectric infrared detecting element having high orientation and a method of manufacturing a thin-film pyroelectric infrared detecting element capable of reducing the size of the element.

[0002]

2. Description of the Related Art In general, a Si substrate is used as an IC substrate. However, in order to achieve miniaturization and high density of a sensor element, a monolithic type in which a transistor circuit and a detection unit (sensor probe) are integrated is used. Must be configured. In this case, the detection unit is formed on the Si substrate. As shown in FIG. 9, a conventional general device has a structure in which a lower electrode 12 is formed on a silicon substrate 10 and a pyroelectric body 14, an upper electrode 16, and a heat absorbing material 18 are formed on the lower electrode 12 in this order. It was done. 20 is a silicon layer (MOS type F
ET element), 22 is a source electrode, 24 is a gate electrode, 2
6 is a drain electrode.

Japanese Patent Application Laid-Open No. 62-822 discloses M
a gO substrate, a thin-film electrode formed on the substrate, a pyroelectric thin film formed on the thin-film electrode, a light-receiving electrode formed on the pyroelectric thin film, and a thin-film transistor formed on the substrate And an infrared detecting element configured such that one end of the thin film electrode is a gate electrode of a thin film transistor.

[0004]

When a lower electrode (for example, Pt) is formed directly on a silicon substrate as in the structure of the conventional device shown in FIG. 9, silicon reacts with the lower electrode material to form a silicide. Cannot be formed, and an electrode thin film suitable for forming a highly oriented sensor material thin film cannot be formed. Therefore, it is necessary to devise a method of forming a buffer layer between the substrate and the lower electrode material. However, it is difficult to obtain a C-axis oriented highly crystalline buffer layer suitable for forming a sensor material thin film. The process becomes complicated. In addition, TFT
In (Thin Film Transistor), glass, quartz, or sapphire is used as a substrate depending on its use. In the case of a TFT, an electrode is generally made of ITO (Indium Tin Oxide). However, it is impossible to form a C-axis oriented sensor material thin film having good crystallinity on the ITO.

Further, even if a Pt electrode is formed on these substrates, for example, quartz and sapphire are made of an electrode material (eg, Pt) because the glass substrate is amorphous.
Therefore, it is impossible to form an electrode suitable for forming a C-axis oriented crystalline pyroelectric thin film. Furthermore, in the conventional film forming method, in order to obtain a thin film crystal having a high C-axis orientation in an as-deposited state, the substrate temperature needs to be higher than 600 ° C. For this reason, a pyroelectric thin film cannot be formed adjacent to the transistor, and it has been impossible to manufacture a small-sized detection element in which the pyroelectric body and the transistor are integrated. The present invention has been made in view of the above points, and an object of the present invention is to provide an infrared detecting element provided with a pyroelectric crystal thin film having high C-axis orientation.
It is another object of the present invention to provide a method for manufacturing an infrared detecting element for forming a pyroelectric thin film at a low temperature (450 ° C. or lower) which does not affect a transistor.

[0006]

In order to achieve the above object, a thin-film pyroelectric infrared detector of the present invention comprises a ceramic single crystal substrate, a lower electrode formed on the substrate, and a lower electrode. A thin-film pyroelectric infrared detection element having a pyroelectric body formed thereon, an upper electrode formed on the pyroelectric body, and a thin film transistor formed on the substrate, The pyroelectric material or / and / or the crystallographic material is used such that the difference between the crystal lattice constant and the crystal lattice constant of the lower electrode is within 3 %.
And Ri Na select the lower electrode material, and the lower electrode material
Lattice Constant and Crystal Lattice Constant of Ceramic Single Crystal Substrate
Lower electrode material or / and so that the difference from the number is within 10%.
And a shall, such by selecting a ceramic single crystal substrate material. When the difference (mismatch) between the crystal lattice constant of the pyroelectric body and the crystal lattice constant of the lower electrode exceeds 3 %, the C-axis orientation ratio is reduced, and the pyroelectric function is disadvantageously reduced.

As described above, the difference between the crystal lattice constant of the lower electrode material and the crystal lattice constant of the ceramic single crystal substrate is 1
The lower electrode material and / or ceramic single crystal substrate material is selected so as to be within 0%, but the difference (mismatch) between the crystal lattice constant of the lower electrode material and the crystal lattice constant of the ceramic single crystal substrate is 10%. In the case of exceeding, the C-axis orientation rate of the electrode material decreases, and this leads to a decrease in the C-axis orientation rate of the pyroelectric crystal formed on the electrode material, so that the pyroelectric function is disadvantageously reduced. .

[0008] The method for manufacturing a thin film pyroelectric infrared detector of the present invention, in fabricating the thin film pyroelectric infrared detection element, by an evaporation method using a laser beam, pyroelectric
Adjacent to pyroelectric thin film without affecting crystallinity
A pyroelectric thin film is formed on a ceramic single crystal substrate at a temperature in the range of 350 to 450 ° C, preferably 370 to 400 ° C, where the characteristics of the transistor are not deteriorated . If the pyroelectric thin film formation temperature is less than the above range, the crystallinity tends to deteriorate, while if it exceeds the above range,
Although the crystallinity of the pyroelectric body does not change or tends to improve, there is a disadvantage that the characteristics of the adjacent transistor deteriorate. In addition, as a ceramic single crystal substrate,
An MgO substrate, a SrTiO ₃ substrate, or the like is used, as the lower electrode, Pt, Nb-doped SrTiO ₃ or the like is used, and as a pyroelectric substance, PbTiO ₃ , LiTaO ₃ ,
LiNbO ₃ , PZT, PLZT or the like is used. In the thin film pyroelectric infrared detection element of the present invention, in particular,
It is preferable that the ceramic single crystal substrate is made of MgO, the lower electrode is made of platinum, and the pyroelectric body is made of PbTiO ₃ .

[0009]

FIG. 1 shows an example of a thin-film pyroelectric infrared detector according to the present invention. 10a is a ceramic single crystal substrate made of MgO or the like, and pt is placed on the substrate 10a.
A lower electrode 12 is formed, a pyroelectric body 14a such as PbTiO ₃ is formed on the lower electrode 12, an upper electrode 16 is formed on the pyroelectric body 14a, and an upper electrode 1 is formed on the pyroelectric body 14a.
6, a heat absorbing material 18 is formed on the
A thin film transistor 30 is formed on a. Reference numeral 20 denotes a silicon layer (MOS type FET element), 22 denotes a source electrode, 24 denotes a gate electrode, and 26 denotes a drain electrode. In the above configuration, the material is selected such that the difference (mismatch) between the crystal lattice constant of the pyroelectric body 14a and the crystal lattice constant of the lower electrode 12 is close to 3 % or less. Further, the difference (mismatch) between the crystal lattice constant of the lower electrode 12 and the expected crystal size of the ceramic single crystal substrate 10a is 10
The material is selected so as to be a value close to within%.

The above-described thin-film pyroelectric infrared detecting element is manufactured by a vapor deposition method using a laser beam by a pyroelectric element 14.
thin film of pyroelectric body 14a without affecting the crystallinity of a
Temperature at which the characteristics of the thin film transistor 30 adjacent to the
Whenever a is 350 to 450 ° C., preferably from 370 to 400
The pyroelectric substance 1 is placed on the ceramic single crystal substrate 10a in the range of
This is performed by forming the thin film 4a. Other steps are the same as the conventional method. Next, an experimental example will be described.
Using MgO substrate as ceramic single crystal substrate, S
i to a thickness of 1 μm and a TFT (Thin Film
Transistor). Figure 2 shows MgO and S
The result of Auger analysis at the interface with the i thin film is shown. The horizontal axis indicates the sputtering time, and the vertical axis indicates the intensity. M
No interdiffusion of gO and Si was observed, indicating that a normal Si thin film was obtained. FIG. 3 shows the transistor characteristics of the TFT formed on the Si thin film. It can be seen that the TFT formed on the MgO substrate also operates normally, similarly to the conventional TFT.

[0011]

【Example】

Example 1 A lower electrode (Pt) was formed on an MgO substrate by RF (high frequency) magnetron sputtering, and a substrate temperature: 380 ° C. and a fluence were formed thereon by excimer laser sputtering.
PbT under conditions of 500 mJ / cm ² , repetition frequency: 10 Hz
iO ₃ (pyroelectric) was deposited. FIG. 4 shows this PbTiO.
The X-ray diffraction measurement results of the _three films are shown. As shown in FIG.
_It can be seen that the _three films are highly C-axis oriented. As a control for FIG. 5, ITO (Indiu) formed on a glass substrate was used.
m TinOxide) PbT film formed on an electrode by excimer laser sputtering under the same conditions as in FIG.
The X-ray diffraction measurement result of the iO ₃ film is shown. In FIG.
No PbTiO ₃ crystal peak is observed. Table 1 shows the crystal lattice constants of MgO, Pt, and PbTiO ₃ for reference.

[0012]

[Table 1]

Embodiment 2 A lower electrode (Pt) connected to a TFT drain electrode is formed by magnetron sputtering (at a substrate temperature of 400 ° C.) (thickness of about 1500) adjacent to the TFT formed by the method of Embodiment 1.
, Area 0.2 mm ² ). PbTiO ₃ was formed thereon by laser ablation (at a substrate temperature of 400 ° C.) to a thickness of about 1.5 μm. After forming Al as a top electrode by a vacuum evaporation method, black paint was spray-coated as a heat absorbing material to prepare a sensor, and it was confirmed that the sensor functions as a pyroelectric sensor.

FIG. 6 shows a schematic diagram of the measuring system in this case. That is, this measurement system includes a blackbody furnace for emitting infrared rays, an optical chopper for intermittently irradiating infrared rays to the pyroelectric element, a frequency analyzer for analyzing an output signal from the pyroelectric element, and a measurement sample. And a pyroelectric element. FIG. 7 shows an example of raw data measured according to FIG. 6 (chopping frequency 10 Hz), and FIG.
From the data obtained in this way, the output voltage with respect to the unit irradiation energy is plotted with respect to the chopping frequency. FIG. 8 shows a typical frequency dependency observed in this type of infrared sensor, and it can be seen that the infrared sensor functions as an infrared sensor.

[0015]

As described above, the present invention has the following effects. (1) The material is selected such that the difference between the crystal lattice constant of the pyroelectric substance and the crystal lattice constant of the lower electrode material is 3 % or less .
First , by selecting a material so that the difference between the crystal lattice constant of the lower electrode and the crystal lattice constant of the ceramic single crystal substrate is 10% or less, the pyroelectric function having a high C-axis orientation can be improved.
A pyroelectric thin film crystal can be obtained. (2) In the thin-film pyroelectric infrared detecting element, the pyroelectricity can be improved by improving the orientation of the pyroelectric crystal. For example, when PbTiO ₃ is used as the pyroelectric body, the pyroelectricity is improved by forming a C-axis oriented thin film crystal. (3) By using a deposition method using a laser beam, the characteristics of the transistors adjacent to the pyroelectric thin film without affecting the crystallinity of the pyroelectric body does not deteriorate 350
A pyroelectric thin film can be formed at a low temperature of 450 ° C. Therefore, a pyroelectric thin film is formed close to the transistor.
And the size of the thin-film pyroelectric infrared detection element can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a thin-film pyroelectric infrared detecting element of the present invention.

FIG. 2 is a graph showing Auger analysis results at an interface between MgO and a Si thin film, and showing a relationship between sputtering time and strength.

FIG. 3 shows a TFT (T) having a Si thin film formed on an MgO substrate.
FIG. 3 is a diagram showing transistor characteristics of a thin film transistor.

FIG. 4 shows a result in Example 1, in which a lower electrode (Pt) is formed on an MgO substrate, and PbTiO is formed thereon.
₉ is a graph showing the results of X-ray diffraction measurement of this PbTiO ₃ film when _three films are formed.

FIG. 5 shows a control of Example 1, in which a PbTiO ₃ film is formed on an ITO (Indium Tin Oxide) electrode formed on a glass substrate.
4 is a graph showing the results of X-ray diffraction measurement of an O ₃ film.

FIG. 6 is a schematic diagram of a measurement system according to a second embodiment.

FIG. 7 is a graph showing signal output data in the second embodiment.

FIG. 8 is an explanatory diagram illustrating sensitivity frequency characteristics in the second embodiment.

FIG. 9 is a cross-sectional view of a conventional general thin film pyroelectric infrared detecting element.

[Explanation of symbols]

 Reference Signs List 10a ceramic single crystal substrate 12 lower electrode 14a pyroelectric body 16 upper electrode 18 heat absorbing material 20 silicon layer 22 source electrode 24 gate electrode 26 drain electrode 30 thin film transistor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01J 1/02 G01J 5/02

Claims (3)

(57) [Claims] A ceramic single crystal substrate; a lower electrode formed on the substrate; a pyroelectric body formed on the lower electrode; an upper electrode formed on the pyroelectric body; A thin-film pyroelectric infrared detection element having the thin film transistor fabricated above, wherein a material is selected such that a difference between a crystal lattice constant of the pyroelectric body and a crystal lattice constant of a lower electrode is within 3 %. Do Te Ri and the lower electrode material crystal skeleton
Between the lattice constant and the crystal lattice constant of a ceramic single crystal substrate
Thin pyroelectric infrared detection element but characterized by Rukoto such by selecting the material such that less than 10%. 2. A ceramic single crystal substrate is made of MgO, the lower electrode is made of platinum, pyroelectric body consists of PbTiO ₃ claim 1 thin pyroelectric infrared sensing element according. 3. The method for producing a thin-film pyroelectric infrared detecting element according to claim 1 or 2 , wherein a vapor deposition method using a laser beam is used without affecting the crystallinity of the pyroelectric body.
A method for producing a thin-film pyroelectric infrared detecting element, comprising: forming a pyroelectric thin film on a ceramic single crystal substrate at a temperature in the range of 350 to 450 ° C. at which the characteristics of a transistor adjacent to the pyroelectric thin film are not deteriorated. .