JPH0721428B2 - Thermal conversion type optical sensor - Google Patents

Description

Detailed Description of the Invention a. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pyroelectric photodetector that absorbs ultraviolet, visible, and infrared light, converts it into heat, and detects the light as a temperature change.

B. 2. Description of the Related Art A heat conversion type optical sensor has a characteristic that wavelength characteristics are flat. Further, since a suitable photoelectric conversion element having sensitivity up to a long wavelength in the infrared region is not known, this type of sensor is widely used. When detecting the same optical power, the pyroelectric type sensor among the thermal conversion type optical sensors has a higher sensitivity when the light is condensed as much as possible and is received by the element having the smallest possible area. That is, when receiving light with an element of a certain area,
Even if the element is divided in half, the output voltage does not change. Therefore, if the same amount of light is concentrated on the element having the half area, the output voltage becomes high because it becomes the same as when the element having the original area is irradiated with the double amount of light. That is, in the case of a pyroelectric sensor, the sensitivity and S / N ratio are improved as the area density of irradiation light is increased.

However, it is difficult to collect light in an arbitrarily small area due to the size of the light source and the convenience of the light collection optical system, and it is said that an element matching the light collection area of the light collected under the given conditions is used. Is the current situation.

C. Problems to be Solved by the Invention In the heat conversion type optical sensor, the heat capacity is preferably as small as possible in order to increase the response speed. In addition, in order to increase the sensitivity, in the case of the pyroelectric type, it is necessary that the temperature rise is large for the same energy input, and this requires a small amount of heat dissipation, so the light is concentrated in a small area. Had to do. From these requirements, the pyroelectric sensor is required to be small, but it is not possible to focus light on an arbitrarily small area because of the convenience of the optical system. Therefore, the present invention intends to improve the sensitivity by using an element smaller than the light concentrating area and by effectively utilizing the light protruding from the area of the element.

D. Means for Solving Problems A light absorption region was formed on a substrate having a low heat conductivity and a small heat capacity, and a pyroelectric detection element was arranged in the light absorption region.

E. Work It is assumed that light is now incident on the entire light absorption area (blackened area). Then, the temperature of the light absorption region is rising. If the light absorption area is removed by leaving only the pyroelectric element here, the pyroelectric element will not have a portion where the ambient temperature has risen and will be directly surrounded by a lower ambient temperature. The temperature will be lower than when there was.
That is, the heat absorption of the pyroelectric element is suppressed by the presence of the light absorption region, and the temperature is higher than that of the pyroelectric element alone. That is, the sensitivity is improved. This is because the heat insulation zone is formed by the light which has passed through the periphery of the pyroelectric element and wasted in the past, thereby reducing the heat radiation of the pyroelectric element and improving the sensitivity.
Since the light absorption region need only have an area and the thickness is not necessary, the substrate can be made as thin as possible within the structurally possible range.
Both the thermal conductivity and the heat capacity can be reduced, and the response speed does not decrease.

F. Embodiment FIG. Shows an embodiment of the present invention.

In FIG. 1, reference numeral 1 is a glass stand in which pillars 2 are set up at four corners,
Mylar films 3 are stretched by supporting the four corners by the columns 2. The mylar film 3 is a 2 mm square and has a thickness of 9 μm. 1.4mm in the center of this mylar film
Platinum electrodes 4 are formed at the corners by sputtering. Platinum black 5 is formed on the surface of this electrode by an electrolytic method to form a light absorption region. As a pyroelectric element, a 0.05 mm square LiTaO ₃ single crystal (Z plate) was sputtered with platinum electrode films on both sides of this platinum electrode, and plates 6 were attached by a conductive adhesive 7. The whole structure was viewed from above. And it is as shown in FIG. The platinum electrode on the upper surface of the Z plate 6 is provided with platinum black similarly to the absorption region. The lead wire 9 is led out from the platinum electrode on the upper surface of the Z plate 6 and the platinum electrode 4 forming the light absorption region.

G. Effect According to the present invention, since a small pyroelectric element is originally installed on a synthetic resin film substrate at a low cost, the cost is low, and the synthetic resin film substrate also serves as a light absorbing region. Even when the element sticks out from the pyroelectric element, the temperature of the substrate surrounding the element rises to keep the element warm, so the heat loss of the pyroelectric element is small in combination with the thin synthetic resin film substrate with low thermal conductivity. The sensitivity is improved compared to the case where the light absorption area is not provided in the same pyroelectric element area, the substrate part is also a film, and the pyroelectric element itself is small, so the heat capacity is small and the response is good, and the environment resistance is low. It is possible to measure with sufficiently high sensitivity and high S / N ratio without ignoring sensitive materials (such as DLATGS).

[Brief description of drawings]

FIG. 1 is a side view of an embodiment of the present invention, and FIG. 2 is a plan view of the same.

Claims (1)

[Claims] 1. A heat conversion type optical sensor comprising a substrate made of a synthetic resin film, a light absorbing region formed on the upper surface of the substrate, and a pyroelectric element disposed in the center of the light absorbing region.