Method of manufacturing sensor and resistor element

Details Method of manufacturing sensor and resistor element Method of manufacturing sensor and resistor element

2000-01-20

2002-05-28

Niebling, John F. (Department: 2812)

Semiconductor device manufacturing: process

Making device or circuit responsive to nonelectrical signal

Thermally responsive

C438S210000

Reexamination Certificate

active

06395575

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to construction and method of manufacturing of electronic components such as infrared sensors for use, for example, in thermometers and human body detecting sensors, and piezoelectric devices for use, for example, in acceleration sensors and the like. In particular, it relates to a method of manufacturing sensors which are useful for electronic components in general in which circuit structures required for impedance conversion by using field effect transistor elements and the like have been mounted, and resistive elements for use in these sensors
BACKGROUND OF THE INVENTION
There exist many electronic components such as various types of sensors which require impedance conversion by means of field effect transistor elements and the like when outputting signal after amplifying a minute signal generated by the sensor.
FIG. 5
shows an impedance conversion circuit employing a sensing element
51
and a field effect transistor element
53
.
In the impedance conversion circuit of
FIG. 5
, sensing element
51
is connected in series with a resistor
52
, and the output of sensing element
51
is connected to the gate of field effect transistor element
53
. In a sensor generating a very small electrical signal, (e.g.,resistor
52
) with a rather high resistance value ranging from several tens of Mohms to several Tohms is used in many cases depending on the type of sensor.
FIG. 6
shows a view illustrating the mounting on a stem of the circuit of FIG.
5
. Four components are to be mounted, namely, a sensing element
61
, a resistive element
62
, a field effect transistor element
63
, and a mounting board
64
. In this configuration, the surface of a stem
65
, which is the substrate for mounting, is covered with a metal, which operates as a grounding (GND) electrode
66
. This is for the purpose of providing protection from external noises. Field effect transistor element
63
is formed on a silicon substrate, and an electrode operating as a gate terminal (G) is formed on the rear surface of the chip whereas a source electrode (S) and a drain electrode (D) are formed on the top surface of the chip.
From the standpoint of circuit configuration, it is impossible to dispose field effect transistor element
63
directly on stem
65
. Consequently, it is first connected via a conductive resin
67
on mounting board
64
which is provided with a connecting electrode on the top surface. While bonding of components other than field effect transistor element
63
does not require a conductive resin, the same conductive resin
67
is generally used for simplifying the mounting process. The connection between electrodes of each elements and substrate electrodes is performed by wire bonding using thin metal wires
68
of Al or Au, and then to an external terminal
69
.
As has been described above, the conventional canned package has as many as four components that need to be mounted, calling for six wires to be wire bonded. Accordingly, the use of many components means not only a high materials cost but also an increase in man-hours for the mounting process resulting in a high cost. Also, as a space is required on the stem, a larger stem is required, thereby making the sensor size larger.
The present invention addresses these issues and aims at realizing a lower sensor cost as well as providing a smaller package.
SUMMARY OF THE INVENTION
In addressing the above issues, the present invention provides a method of manufacturing a sensor comprising a resistive element having a top surface electrode and a bottom surface electrode, a sensing element generating an electrical signal by sensing energy from the outside, a field effect transistor element on the rear side of the chip of which a gate electrode is formed, and a substrate having a first electrode, a second electrode, and a third electrode on its top surface, the method comprising the steps of electrically connecting the bottom surface electrode of the resistive element and first electrode of the substrate, electrically connecting the field effect transistor element onto the resistive element so that the gate electrode and a portion of the top surface electrode of the resistive element meet, electrically connecting one of the electrodes of the sensing element and a portion of the top surface electrode of the resistive element, electrically connecting the source and drain electrodes of the field effect transistor element respectively to the second electrode and the third electrode on the substrate, and electrically connecting the other electrode of the sensing element to the first electrode on the substrate. With this invention, the mounting board of the prior art example becomes unnecessary and the number of wires is reduced from 6 to 4 thereby reducing the cost. Also, as a resistive element is disposed at a position where a mounting board is disposed in the prior art, the space occupied by the resistive element becomes unnecessary thus providing a smaller package.
The present invention also provides a sensor in which the resistive element of the above described sensor is formed with a ceramic material, glass material, or the like, or ferrite material, and in which a resistor body having a relatively high resistance value in the range from several tens of Mohms to several Tohms can be formed with ease.
The present invention also provides a method of manufacturing a resistive element having a predetermined resistance value by forming in advance an electrode over the entire top and bottom surfaces of a flat resistor body with a large area and cutting to arbitrary dimensions after measuring the resistance value. According to this invention, as the resistance value is inversely proportional to the area of the electrode, it is possible to change the resistance value by the size to be cut based on the resistance value measured in advance when the area is large, thereby allowing formation of a resistive element having a precise resistance value which is intended to be obtained after cutting. Also, by changing the area to be cut, it is possible to obtain resistive elements having many types of resistance values from the same resistor body. Furthermore, it is a method of manufacturing with superiority in mass producibility as it is possible to configure a continuous mounting process from cutting to mounting by employing a cutting method such as dicing or the like. The present invention also provides a method of manufacturing resistive elements in which the resistor body to be used for the resistive elements is formed at a sintering temperature such that the rate of water absorption becomes 1% or less. According to this invention, even when a process in which cutting of the resistor body to be used for resistive elements is diced while water is being sprayed, no change in the resistance value due to water absorption or moisture absorption by the resistor body occurs. It is also possible to realize a high reliability resistive elements as no change in the resistance value is caused even under a high-temperature, high-humidity environment.
Furthermore, in the present invention, the method of manufacturing the above described sensor is one in which the resistive element is simply a resistive element of which the electrodes are formed on the top and bottom surfaces of the resistor body, a first electrode on a substrate is electrically connected with the bottom surface electrode of the resistive element via an conductive material, and a predetermined resistance value is obtained by controlling the amount of the conductive material so as to control the amount of resin which rises on the sides of the resistor body. With this invention, it is possible to correct the resistance value by controlling only the amount of resin to be coated even when there is some variation in the obtained resistance values among production lots.
The present invention also provides a method of manufacturing a resistive element having a predetermined resistance value in which the resistance value is controlled by heat treating a

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