Infrared detector

An infrared detector has a sensor with an infrared detecting portion composed of a thermal sensitive resistor film on an insulating film provided on a surface of a semiconductor substrate. The sensor is installed on a base such that it bridges a cavity in the substrate. The cavity is sealed by an infrared reflecting film or an infrared reflecting metallic board.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to an infrared detector which is a noncontacting 
temperature sensor for detecting infrared radiation by using a change in 
resistance of a thermal sensitive element caused by a change of 
temperature. 
2. Description of the Prior Art 
Previously, a thermal type infrared detector is known as one example of 
infrared detectors for detecting a surface temperature of an object with 
noncontacting detection. 
The thermal type infrared detector is a sensor for measuring a surface 
temperature of the object under high temperature and the moving object 
with noncontacting condition. The temperature of the thermal sensitive 
element is raised by the energy of incident infrared rays radiated from 
the object to be detected. The surface temperature of the object to be 
detected is measured by capturing the change in electric resistance of the 
thermal sensitive element due to the change of temperature. 
Generally, a thermistor made of the transition metal oxides in which the 
resistance value is changed depending on the temperature and a thin film 
metallic resistance material or thin film thermocouple are used for the 
thermal sensitive element of the infrared sensor. 
Usually, since the infrared ray dosages radiated from the object to be 
detected are weak, the following matters are required: 1 a thermal 
capacity for the thermal sensitive element of the sensor should be small, 
2 infrared radiation absorption characteristic for the thermal sensitive 
element of the sensor should be good, and 3 high accurate element 
manufacturing technology is required. 
From such a standpoint, there has been developed an infrared sensor 
provided with the thermal sensitive element such as a thermistor of the 
amorphous silicon type or the like at the infrared detecting portion 
thereof supported by means of the micro-bridge on the cavity formed on the 
silicon substrate. 
However, even if the infrared detector has such a construction, since the 
infrared rays are weak, sufficient sensitivity cannot be obtained. For the 
above reasons, an infrared detector which is improved in light of these 
drawbacks is proposed. For example, Japanese Patent Application Laid Open 
No. Hei 6-137935 has disclosed a thermal type infrared detector using a 
similar thin film resistor. 
The explanations thereof are given with referring FIG. 4. The infrared 
detector comprises the infrared sensor of which the cavity is formed 
within the substrate is placed on the base 2. The infrared detector is 
provided with the infrared detecting portion 11 composed of the resistor 
layer having the pair of electrodes on the insulation thin film supported 
by the crossbridging construction on the substrate 10. The insulation 
layer 12 of reverse side of the substrate 10 is fastened to the basement 2 
with adhesive bonding. The recess 6 is provided for the base 2 the 
position of which is opposite to the infrared detecting portion 11. 
Further the terminal 8 which is penetrated into the base 2 is provided. 
The terminal 8 is connected to the electrode 13 of the infrared sensor by 
means of the wire 9. The reference numeral 4 shows the cover body roofing 
the infrared sensor. A filter 3 is provided for the cover body. 
The recess 6 is formed on the base 2 of the infrared detector so that the 
clearances to the infrared detecting portion 11 are of one depth of the 
recess 6 distant from the base 2. Since the gases intervene between the 
infrared detecting portion 11 and the base 2, the heat conduction between 
the infrared detecting portion 11 and the base 2 is lessened. It renders 
the thermal capacity of the infrared detecting portion 11 low value 
thereby in causing the thermal insulation property to make good. The 
sensitivity of the infrared sensor is improved over the conventional case. 
In the conventional infrared detector, in the case that the thermal 
conductivity of the surface of base is large, heat which moves from the 
detector toward the base increases with heat transfer, thereby the 
temperature rise of the infrared sensor is decreased. For the above 
reasons, it causes the thermal insulation property of the infrared 
detecting portion to enhance by providing the recess on the base portion 
which is opposite to the infrared detecting portion. 
However, there are drawbacks in which accurate temperature detection can 
not be performed in that even if the thermal insulation property enhanced 
by enlarging the spacing between the base and the recess, if the material 
for the base has high emissivity, it renders the output of the infrared 
detecting portion influential. 
Further, there are drawbacks in which even if the accurate temperature 
detection is possible, substantial improvement of the detecting 
sensitivity can not be desired, because even if the material for the base 
has low emissivity, only it is not influenced by the radiant heat from the 
base. 
SUMMARY OF THE INVENTION 
In view of the foregoing, it is an object of the present invention to 
provide an infrared detector which can improve a detecting sensitivity and 
a detecting efficiency by receiving the infrared rays efficiently radiated 
from the object to be detected. 
According to the first aspect of the present invention, for achieving the 
above-mentioned object, there is provided an infrared detector having an 
infrared detecting portion composed of a thermal sensitive resistor film 
on an insulating film provided for one surface of a semiconductor 
substrate, a cavity formed within said substrate, an infrared sensor which 
makes said infrared detecting portion a crossbridging construction, 
installed on a base, a recess formed on a portion which is opposite to 
said infrared detecting portion, resting on said base on which said 
infrared sensor is placed, and an infrared reflecting film provided for at 
least a bottom surface of said recess. 
According to the second aspect of the present invention, there is provided 
an infrared detector having an infrared detecting portion composed of a 
thermal sensitive resistor film on an insulating film provided for one 
surface of a semiconductor substrate, a cavity formed within said 
substrate, an infrared sensor which makes said infrared detecting portion 
a crossbridging construction, installed on a base, a penetration formed on 
a portion which is opposite to said infrared detecting portion, resting on 
said infrared sensor of said base on which said infrared sensor is placed, 
and an infrared reflecting film for sealing said penetration from outside 
of said base. 
According to the third aspect of the present invention, there is provided 
an infrared detector having an infrared detecting portion composed of a 
thermal sensitive resistor film at an insulating film provided for one 
surface of a semiconductor substrate, a cavity formed within said 
substrate, an infrared sensor which makes said infrared detecting portion 
a crossbridging construction, installed on a base, a curved recess formed 
on a portion which is opposite to said infrared detecting portion, resting 
on said base on which said infrared sensor is placed, and an infrared 
reflecting film provided for an inner surface of said curved recess. 
According to the fourth aspect of the present invention, there is provided 
an infrared detector of the above-described second aspect wherein an 
infrared reflecting board which is of high infrared reflection factor made 
of metallic board is substituted for said infrared reflecting film. 
As described hereinbefore, the infrared detector according to the present 
invention causes the temperature of the thermal sensitive resistor film of 
the infrared detecting portion to rise by injection of the infrared rays 
emitted from the object to be measured. The infrared rays reflected by the 
infrared reflecting film provided on the inner surface of the recess of 
the base can impose a temperature rise of the thermal sensitive resistor 
film. Detecting sensitivity of the infrared detector is improved since the 
thermal insulation between the infrared detector and the base is good 
caused by the fact that the space between the infrared detecting portion 
and the base becomes large. 
Further, it causes the detecting sensitivity to be improved, since it is 
capable of irradiating the infrared rays toward the infrared detecting 
portion by virtue of causing the infrared reflecting film to be curved. 
Furthermore, it causes detecting sensitivity to be improved, since the 
infrared reflecting board with high infrared reflecting factor is 
substituted for the infrared reflecting film. 
The above and further objects and novel features of the invention will be 
more fully understood from the following detailed description when the 
same is read in connection with the accompanying drawings. It should be 
expressly understood, however, that the drawings are for purpose of 
illustration only and are not intended as a definition of the limits of 
the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A preferred embodiment of the infrared detector according to the present 
invention will now be described in detail referring to the accompanying 
drawings. 
FIG. 1A is a plan view showing an embodiment of an infrared detector 
according to the present invention, and FIG. 1B is a sectional view of the 
infrared detector of FIG. 1A, taken along line I--I thereof. 
In FIGS. 1A and 1B, reference numeral 1 designates an infrared sensor 
placed on a base 2. In the infrared sensor 1, an electrode portion thereof 
is connected to a terminal 8 by means of a wire 9. The infrared sensor 1 
placed on the base 2 is sealed by a cover body 4 provided with a filter 3. 
A collimator 5 is provided around the cover body 4. 
A substrate 10 for the infrared sensor 1 is fastened on the base 2 which is 
made of metal or synthetic resin or the like by means of adhesives such as 
for example low-melting glass, eutectic alloy (Au--Si), solder or the 
like. The terminal 8 and the electrode of the infrared sensor by which the 
base 2 is penetrated are bonded by the wire 9. It is also good to wire by 
using lead frame and so forth. In the base 2 on which the infrared sensor 
is placed, the recess 6 is formed thereon opposite to the infrared 
detecting portion of the infrared sensor 1. 
On an inside surface of the recess 6, in particular, there is provided an 
infrared reflecting film 7 for the base. A material in which emissivity is 
small and reflection factor is large is used. For example, gold or 
aluminum is good to use. An open area of the recess 6 is at least larger 
than that of the infrared detecting portion of the infrared sensor 1. 
The infrared sensor 1 is composed of insulating films 11a, 11b made of 
silicon nitride or silicon oxide formed at obverse surface and reverse 
surface of the silicon substrate 10, a insulating film 12 made of aluminum 
oxide or tantalum oxide which is provided on the insulating film 11a, a 
pair of metal base layers 13 made of tantalum (Ta), titanium (Ti), 
chromium (Cr), molybdenum (Mo) and the like which are provided for the 
insulating film 12, an insulating film 14 made of silicon oxide provided 
between the pair of metal base layers 13, at least one layer of thermal 
sensitive resistor film 15 formed on the insulating film 14, a pair of 
electrode layer 16 made of platinum (Pt) which come into contact with the 
thermal sensitive resistor film 15 formed oppositely to each other, a 
protective insulating film 17 provided on the thermal sensitive resistor 
film 15, and a buffer film 18 made of tantalum oxide or titanium oxide 
intervening between the protective insulating film 17 thereunder and a 
glass layer 19 made of borosilicate glass thereon. The cavity is formed 
within the substrate corresponding to the infrared detecting portion by 
the technique of etching. The infrared detecting portion is constituted as 
the crossbridging construction. 
The base 2 on which the infrared sensor 1 is placed fixedly is sealed by 
covering with the cover body 4 made of metal or the like. When necessary 
an internal space thereof is sealed, with inert-gas filled or under 
reduced pressure. An aperture is provided for an upper surface of the 
cover body 4, an optical filter 3 is attached thereto. Single crystal 
silicon, glass, transparent synthetic resin or the like each of which has 
high transmittancy for the infrared rays to be detected is used. 
A collimator 5 made of aluminum the properties of which are large thermal 
conductivity, small infrared emissivity, and high infrared reflection 
factor is installed around the cover body 4. The shape of the collimator 5 
is selected as they see fit depending on size and temperature of the 
object to be measured or distance thereof. It is capable of detecting 
accurately the infrared rays of the object to be detected aim at detection 
by virtue of providing the collimator 5. 
In the infrared detector of the above described embodiment, the temperature 
at that time is measured in such a way that it causes the infrared rays 
with constant energy irradiated from the black body furnace to irradiate 
through the filter surface toward the thermal sensitive resistor film. As 
a result thereof, the value is 0.9 m.degree.C./.mu.W under the exception 
of the infrared reflecting film, and the value is 1.2 m.degree.C./.mu.W 
under forming the infrared reflecting film 7 as the embodiment. Namely, It 
has been proved that high output sensitivity can be obtained in that the 
infrared energy is effectively transformed to heat energy at the infrared 
detecting portion. 
Of course, this improvement of detecting efficiency does not depend on the 
infrared sensor but effect by virtue of the infrared reflecting film 7, 
accordingly it is obvious to obtain the same effect even if conventional 
infrared sensor of crossbridging construction is used. 
Next, it will be described the another embodiment of the infrared detector 
according to the invention referring to FIGS. 2A, 2B and 2C. FIG. 2A is 
the plan view showing the another embodiment of the infrared detector 
according to the present invention, FIG. 2B is the sectional view of the 
infrared detector of FIG. 2A, taken along line II--II thereof. 
In FIGS. 2A, 2B and 2C, the infrared detecting portion of the infrared 
sensor 1 has the crossbridging construction which is different from the 
infrared sensor according to FIG. 1. The same infrared sensor as FIG. 1 
can be permitted. The recess 6 is formed on the base 2, a curved surface 
2A is formed on the bottom thereof, and the infrared reflecting film 7A is 
provided for the inner surface of the curved surface 2A. 
Thus, by making the infrared reflecting film 7A curved, since the infrared 
rays reflected at the infrared reflecting film 7A are converged on the 
infrared detecting portion 20, higher output sensitivity can be obtained. 
In the infrared sensor 1, an insulating film 21 is formed on the reverse 
side of the substrate 10, the electrode 22 of the infrared sensor 1 is 
connected to the terminal 8 by means of the wire 9. 
A shape of curved surface for the infrared reflecting film 7A and 
establishment of a distance between the infrared detecting portion 20 and 
the curved surface can be decided depending on an effective area of the 
infrared detecting portion and conditions of the incident infrared ray. 
Further in FIG. 2C, a curved recess 2A is formed on the base 2 of the 
infrared detector, on the inside surface thereof the infrared reflecting 
film 7A is provided. Thus such configurations yield the same effect as the 
above described ones. 
Next, it will be described the another embodiment of the infrared detector 
according to the invention referring to FIGS. 3A, 3B. FIG. 3A is the plan 
view showing the another embodiment of the infrared detector according to 
the present invention, FIG. 3B is the sectional view of the infrared 
detector of FIG. 3A, taken along line III--III thereof. 
In FIGS. 3A and 3B, a penetrated portion 6A is provided for the base 2 
instead of providing the recess, it causes a substrate 14 on which the 
infrared reflecting film 7B is formed to insert into the penetrated 
portion 6A from the basement 2, with the penetrated portion 6A sealed. As 
described above, gold or aluminum thin film is used for the infrared 
reflecting film 7B, it does not necessarily use the infrared reflecting 
film, it is good for use a board like configuration as an aluminum board. 
Further, the infrared sensor 1 is effective if it has simply the 
crossbridging construction, it is not necessarily to be the infrared 
sensor as shown in the embodiment of FIG. 1. 
As described above, in the infrared detector according to the present 
invention, since the recess or the curved recess is formed at the base 
directly under the infrared detecting portion, the infrared reflecting 
film with high infrared reflecting factor is formed thereon, the infrared 
rays which transmits the infrared detecting portion of the infrared sensor 
is reflected at the infrared reflecting film and the infrared rays 
irradiate the infrared detecting portion twice. There are advantages that 
the detecting efficiency rises and it is capable of improving the output 
sensitivity. 
Further, regardless of the shape of the base in particular, the thickness 
thereof, it has similar effect of the infrared detector of which the 
reflecting film is formed on the bottom surface of the base, since it is 
capable of determining distance between the infrared detecting portion and 
the base by providing the penetration for the base. 
Further, there is advantage that it is capable of further rising the 
detecting sensitivity by converging the incident infrared rays at the 
infrared reflecting surface with curved surface, and by virtue of causing 
the infrared detecting portion to transmit by forming the curved surface 
at the reflecting surface. 
While preferred embodiments of the invention have been described using 
specific term, such description is for illustrative purpose only, and it 
is to be understood that changes and variations may be made without 
departing from the spirit or scope of the following claims.