Pyroelectric infrared array sensor

Details Pyroelectric infrared array sensor Pyroelectric infrared array sensor

1998-05-13

2001-01-16

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Infrared responsive

C250S332000

Reexamination Certificate

active

06175114

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a pyroelectric infrared array sensor which senses infrared rays, for example, from a human body, and generates an alarm signal.
2. Description of the Related Art
A pyroelectric infrared array sensor utilizes a sensing element comprising a material such as PZT (lead zirconate titanate) having a pyroelectric effect. The term “pyroelectric effect” as used herein is intended to mean the characteristic that, when infrared rays are applied to the sensing element, the surface temperature of the latter is changed, as a result of which the charges therein are no longer in the state of neutralization; that is, the element becomes electrically unbalanced, thus producing charges. The charges thus produced can be converted to a voltage by an impedance circuit.
An example of a circuit for use in the pyroelectric infrared array sensor is shown in
FIG. 1. A
sensing section
1
is formed on a pyroelectric element, and is connected in parallel to a high-resistance chip
2
. One of the terminals of the high-resistance chip
2
is connected to the gate terminal G of an FET (field-effect transistor)
3
, and the other terminal is grounded. When a positive voltage is applied to a drain terminal pin
4
connected to the drain terminal D of the FET
3
, charges produced in response to the application of infrared rays to the sensing section
1
can be detected as a voltage output at a source terminal pin
5
connected to the source terminals of the FET
3
.
This characteristic is utilized to provide a pyroelectric infrared linear array sensor in which a plurality of sensing sections are arranged in a line, or a pyroelectric infrared two-dimensional array sensor in which a plurality of sensing sections are arranged two-dimensionally. Those sensors are used for detecting the position or the direction of movement of a person or the like.
FIG. 2
is an exploded perspective view of a conventional pyroelectric infrared array sensor. Terminal pins
6
are embedded in a metal header
8
in such a manner that they penetrate the header
8
through insulating cylindrical pieces
7
. A grounding pin (not specifically indicated) is formed by applying conductive paste to the insulating cylindrical piece
7
of a selected one of the terminal pins
6
, thereby shorting the terminal pin
6
to the metal header
8
, to form the desired grounding pin.
The terminal pins
6
protruding from the upper surface of the metal header
8
are inserted into holes
10
formed in a substrate
9
, respectively, and fixedly connected to lands (not shown) which are connected to a circuit (not shown) formed around the holes
10
.
A pyroelectric element
11
is mounted via solder bumps
16
on the upper surface of the substrate
9
, and high-resistance chips
2
and FETs
3
are mounted on the upper and lower surfaces of the substrate
9
. The number of the high-resistance chips
2
and the number of the FETs
3
is equal to the number of the sensing sections.
A casing
12
has an opening
13
which confronts the pyroelectric element
11
. The opening
13
is covered by an infrared filter
14
.
The metal header
8
is electrically welded to the casing
12
, so that the header
8
is electrically connected to the casing
12
.
The pyroelectric element
11
is polarized in advance so that its one side is positive, and the other side is negative. The light receiving surface of the pyroelectric element
11
confronts the infrared filter
14
which is perpendicular to the axis of polarization.
As shown in
FIG. 3
, a plurality of upper electrodes
15
A are provided on the light receiving surface of the pyroelectric element
11
, and a plurality of lower electrodes
15
B are provided on the opposite surface of the element
11
in such a manner that the electrodes
15
B confront the electrodes
15
A, respectively, through the element
11
, thus providing a plurality of sensing sections each including a pair of electrodes
15
A and
15
B. The electrodes
15
A of the sensing sections are connected to one another with connecting conductors
15
C. In addition, lead conductors
15
D are formed on the element
11
. The electrodes
15
A, thus connected to each other, are connected to the circuit on the substrate
9
through the lead conductors
15
D. The electrodes
15
A and
15
B, the connecting conductors
15
C, and the lead conductors
15
D are formed in this example by vapor deposition of NiCr, Ag, Ag—Cu or the like. In the case where the electrodes
15
A and
15
B are formed of Ag or Ag—Cu, a black film is formed on the surface of each of the electrodes
15
A, which absorbs heat with high efficiency.
In order to prevent heat generated at the sensing sections of the pyroelectric element
11
from flowing to the substrate
9
, the pyroelectric element
11
is held spaced from the substrate
9
; that is, it is secured by the electrodes
15
B to solder bumps
16
formed on the circuit on the substrate
9
by using conductive paste
17
. Each of the electrodes
15
B is connected through the circuit on the substrate
9
to one terminal of the respective high-resistance chip
2
and to the gate terminal of the respective FET
3
(see FIG.
1
). The upper electrodes
15
A are connected to one another by the connecting conductors
15
C, and are fixedly connected through the lead conductors
15
D to conductive parts such as the solder bumps
16
on the circuit of the substrate
9
by conductive paste
17
A, and are thereby connected to the grounding pin and to the remaining terminals of the high-resistance chips
2
(see FIG.
1
). The drain terminals and source terminals of the FETs
3
are connected to predetermined ones of the terminal pins
6
.
Charges produced by the plurality of sensing sections of the pyroelectric element
11
are detected as a voltage by a plurality of impedance conversion circuits made up of the FETs
3
. By comparing the different outputs of the plurality of sensing sections with one another, the direction of movement or position of a person or the like can be detected.
In the case of a pyroelectric infrared two-dimensional array sensor which includes sixteen (4×4) sensing sections
18
through
33
as shown in FIGS.
4
(
a
) and
4
(
b
), the sensing sections
18
,
21
,
30
and
33
at the four corners are each adjacent to two sides of the rectangular pyroelectric element
11
, and therefore they are high in thermal resistance. Hence, it is difficult for the heat generated at those sensing sections by infrared rays to diffuse. The sensing sections
19
,
20
,
22
,
25
,
26
,
29
,
31
and
32
are provided along respective sides of the pyroelectric element
11
. Therefore, the heat generated at the sensing sections
19
,
20
,
22
,
25
,
26
,
29
,
31
and
32
is more easily diffused than the heat generated in the sensing sections
18
,
21
,
30
and
33
. Hence, the sensing sections
18
,
21
,
30
and
33
are highest in sensitivity, and the sensing sections
19
,
20
,
22
,
25
,
26
,
29
,
31
and
32
are lower in sensitivity.
The sensitivity of the sensing sections
22
and
26
may be further reduced by thermal conduction through the lead conductors
15
D to the conductive parts on the substrate
9
such as the respective solder bumps
16
that are connected to ground.
The conventional pyroelectric infrared two-dimensional array sensor has problems related to these variations in sensitivity. Hence, in application of the sensor, the amplification factors of the amplifier circuits for all the sensing sections must be adjusted; in other words, the adjustment must be carried out for every sensing section, which takes a lot of time and labor, and increases the manufacturing cost of the sensor.
In a pyroelectric infrared linear array sensor as shown in FIGS.
5
(
a
) and
5
(
b
) in which a plurality of sensing sections are arranged one-dimensionally, as in the case of the pyroelectric infrared two-dimensional array sensor, the sensing sections at both ends of the pyroelectric element
11
are highest in sensitivity. The remai

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