JPH0447606A - Pyroelectric type infrared sensor - Google Patents

Abstract

PURPOSE:To increase a figure of merit and a specific detectability by providing a Pt film [001]-oriented on a substrate which has a larger coefficient of thermal expansion than that of a thin film of specific composition and of which mismatching ratio with a lattice constant of the thin film is not more than 10%, and also utilizing a ferroelectrics thin film having [001]-orientation and the particle diameter of 1mum or more as a thin film having specific composition, being formed over the Pt film. CONSTITUTION:A substrate 3 to be required is to have a larger coefficient of thermal expansion than that of a thin film represented by a chemical formula of Pb(Zr1-xTix)O3 and 10% or below the mismatching ratio with a lattice constant of the thin film represented by the formula of Pb(Zr1-xTix)O3. An MgO single crystal is taken, for example, because of heightening [001]-orientation ratio. Next, a Pt film 2 [001]-oriented is formed as a conductive film by which a lower electrode in a pyroelectric type infrared sensor is made. Composition of the Pt film 2 represented by the chemical formula of Pb(Zr1-xTix)O3 is for making [001]-orientation and a value of (x) in the formula is set within the range of 0.48<=x<=1, and also the particle diameter is set not less than 1mum. Because of such a high orientation property and the effective particle diameter, the dielectric constant becomes small, and the figure of merit and the specific detectability become large.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pyroelectric infrared sensor using a ferroelectric thin film.

Conventional devices for detecting infrared rays include quantum type and thermal bath. The quantum type has the characteristics of fast response speed and high sensitivity, but requires cooling and has a limit to the detection wavelength. On the other hand, the pyroelectric type, which belongs to the thermal bath category, has low sensitivity but has the advantage of operating at room temperature and having no wavelength dependence on sensitivity.

In this pyroelectric element, the performance is improved by reducing the heat capacity by making the pyroelectric material thinner in order to increase the response speed. In terms of characteristics, attempts have been made to improve the properties by thinning the ferroelectric material using sputtering. However, in terms of specific detectability, it is about 2×10'cm 5 /W, which is comparable to that of a pyroelectric element using a bulk material, and an element with even better characteristics in terms of sensitivity and detectability is desired.

An object of the present invention is to provide a pyroelectric infrared sensor with a high figure of merit and high specific detection ability.

The present invention uses the chemical formula P b (Z r, -xT ix)
On a substrate, the coefficient of thermal expansion is larger than that of the thin film represented by o, and the mismatch rate with the lattice constant of the thin film represented by the chemical formula pb(Z r, -xT i,) is 10% or less. [0
01] having an oriented Pt film and further formed on the Pt film with the chemical formula P b (Z r, -, T ix) O,
This is a pyroelectric infrared sensor using a ferroelectric thin film having a composition of 0.48≦X≦1 or having a [001] orientation and a grain size of 1 μm or more.

In order to increase the sensitivity of a tongue-and-mouth pyroelectric infrared sensor, what is required is a large pyroelectric coefficient and a small dielectric constant. Furthermore, in order to increase the specific detectability, the figure of merit must be large and the noise must be small.

The ferroelectric thin film used in the device of the present invention has the chemical formula Pb (
The coefficient of thermal expansion is larger than that of the thin film represented by Z r, -, T i j O, and the chemical formula P b (Z r, - x T i
x) The mismatch rate with the lattice constant of the thin film represented by o is 1
0% or less is required. For example, MgO single crystal. This is to increase the [001] orientation rate.

Next, a [001]-oriented Pt film was formed as a conductive film to serve as a lower electrode in a pyroelectric infrared sensor.

Although it is possible to use other than pt, the chemical formula Pb(Zr, Ti
, )O, the mismatch rate with the lattice constant of the thin film is small, and the chemical formula p b (z r, -xT i,)○3
It is necessary that the reaction does not occur at the thin film formation temperature expressed by . Next, as a method for forming a ferroelectric film, it is preferable to use a method that allows crystal grain size to grow appropriately, and in the present invention, a CVD method that grows in a state close to thermal equilibrium and causes less damage to the surface is adopted. Even the sputtering method is possible by controlling the growth rate and cooling rate. The composition of the thin film represented by the chemical formula Pb(Zrl-xT 1x)O is for [001] orientation. In addition, in the above chemical formula, X is 0.4.8≦
The range is X≦1. This is because it is preferable to have a tetragonal crystal.

The ferroelectric thin film obtained by this method has a [:OO1] orientation ratio of 0.85 or more, and can have a low dielectric constant. Further, as shown in FIG. 3, the relative permittivity changes depending on the particle size, and the relative permittivity can be reduced at 1 μm or more. If abnormal grain growth occurs, the flatness of the film will be impaired, so a range of 1 μm to 3 μm is more preferable. Due to the effects of this high orientation and particle size, the relative permittivity becomes small, and the figure of merit expressed by the ratio of the pyroelectric coefficient to the relative permittivity increases. Also,
Since the dielectric loss noise expressed by the following equation is also small, the noise becomes small, and the specific detection ability expressed as the ratio of sensitivity to noise becomes large.

K: Boltzmann constant T ・Absolute temperature ω: Angular frequency of infrared rays R: Electrical resistance ε0: Dielectric constant of vacuum A: Infrared receiving area d: Thickness τ6: Electrical time constant tanδ ° Dielectric loss, Relative permittivity Examples This invention The ferroelectric thin film in [001] oriented M
After forming Pt oriented in the [OO1] direction, which will become the lower electrode, on the g◯ substrate by high-frequency sputtering, it was formed on the Pt by CVD. The thickness of the lower electrode PL is 0.1μ
m, and the ferroelectric thin film is pb(C,H,)4, Z r
(DPM) 4, T j, (i-QC, H,).

was used as a raw material, and synthesis was carried out under the conditions shown in Table 1.

Table Carrier gas flow rate is 20 to 100 m1/m for each raw material
Adjust m according to the Zr/Ti composition ratio with i n, and
A film with a thickness of about 2 μm was formed in 0 minutes.

The particle size of the obtained thin film was 1 μm or more.

As a result of X-ray diffraction, in the ferroelectric thin film formed on the [001]-oriented Pt, only reflections from the (1,00) plane and the (ooi,) plane were observed. The orientation ratio α of the thin film in the [001] direction is (■) when the reflection intensities of the (100) plane and (00], ) plane are respectively (■1o, T, . . . ). .

■1°. Ten ■. .

Defined by

Next, in order to investigate the characteristics of the obtained ferroelectric thin film,
A layer of Au having a thickness of μrn is formed by vapor deposition to serve as the upper electrode,
at 25 °C], OO] (2 at an electric field strength of V/cm
The pyroelectric coefficient and relative dielectric constant were measured after performing a 0-minute poling process. Table 2 ■ to ■ show the [001] orientation ratio α, relative permittivity ε1, and pyroelectric coefficient λ of the ferroelectric thin films produced according to the present invention.
, figure of merit λ/ε0ε1, l Comparative four-state performance D at OHz
For comparison, the values of JP-A-60-131704 manufactured by the sputtering method are shown. The reason why the dielectric constant of the comparative example is large is considered to be because the crystal grain size is small.

Margin below? The ferroelectric thin film formed on the [001] oriented P film is
Since the [001] orientation rate is 85% or more and the dielectric constant ε1 is small, the figure of merit becomes significantly large.

Especially 7. ε in a composition with a large amount of r is greatly improved. Further, dielectric loss noise is also reduced, and specific detection ability is increased.

FIG. 1 shows an example of manufacturing a pyroelectric infrared sensor using this ferroelectric thin film. The method for manufacturing this device is to first use photolithography technology to place a 1,5
, 5mm' pattern was formed, and the lower electrode was formed by high-frequency sputtering on the leftover part [
001] direction was formed to a thickness of 0.1 μm. Next, a ferroelectric thin film was formed on Ptl by CVD. The ferroelectric thin film is P b (C, H,), Z
Using r (D P M) 4, T1 (1-○C3H,) 4 as raw materials, synthesis was carried out for 200 minutes under the conditions shown in Table 1 to form a film with a thickness of 2 μm.

Next, in order to reduce the heat capacity of the device, a pattern was formed on the lower part of the MgO substrate using a four-lithography technique, and then etched using an ion milling method to form a space under the light receiving section.

Next, 200 pieces of NiCr, which will become the upper electrode, were formed on the ferroelectric thin film by vapor deposition, and after forming a pattern using photolithography to match the lower electrode of the PL, unnecessary parts were etched using ion milling. . It goes without saying that ion milling was used for etching the MgO substrate and ferroelectric thin film, or wet chemical etching or reactive ion etching could be used.

Attach this to the metal package with insulating adhesive,
Next, in order to extract the pyroelectric current generated by the incidence of infrared rays as a voltage change, an impedance conversion FET is bonded, and wires are wired between the FET electrode and the upper electrode and between the posts of the metal package using the wire bonding method, and the wavelength of the incident infrared rays is A pyroelectric infrared sensor was installed with a cap with a filter to limit the amount of heat generated.

FIG. 2 shows - as an example P b (Z r,, T I.6
) Light-receiving area made using a thin film with a composition of 03: 2.25
This figure shows the voltage sensitivity Rv and ratio detection capability of a single element of mm2. The specific detection ability is more than an order of magnitude larger than that of the 2×10°cm FT/W rebulk.

The present invention is not limited to the above-mentioned embodiments. For example, by arranging infrared light receiving sections two-dimensionally, it is possible to detect two-dimensional infrared light with high sensitivity using an element with a small area for each light receiving section. It is possible.

As explained above, the pyroelectric infrared sensor of the present invention has a structure in which the ferroelectric thin film is formed by orienting the ferroelectric thin film on the oriented lower electrode and by controlling the particle size. The dielectric constant becomes smaller and the figure of merit becomes significantly larger. Therefore, a highly sensitive sensor can be obtained even if the light receiving section is small. This allows extremely excellent characteristics to be provided not only when manufacturing a single sensor but also a two-dimensional array sensor.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a pyroelectric infrared sensor light receiving section according to an embodiment of the present invention. In FIG. 1, 1 is a ferroelectric thin film, 2 is a lower electrode (Pt), 3 is an MgO substrate, 4 is a J-FET, and 5 is an upper electrode (NiCr). FIG. 2 shows voltage sensitivity (RV) and specific detectability (D*) in embodiments of the present invention. Figure 3 shows the relationship between the grain size and dielectric constant of a thin film.

Claims (1)

[Claims] The coefficient of thermal expansion is larger than that of the thin film represented by the chemical formula Pb(Zr_1_-_xTi_x)O_3;
[001
] oriented Pt film, and further formed on the Pt film, with the chemical formula Pb(Zr_1_-_xTi_x)O_3, and 0.
A pyroelectric infrared sensor using a ferroelectric thin film, characterized in that the thin film has a composition of 48≦x≦1, is oriented in [001], and has a grain size of 1 μm or more.