Methods of producing resistor elements

Details Methods of producing resistor elements Methods of producing resistor elements

2000-03-09

2002-12-24

Pourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making passive device

Resistor

C338S0220SD, C338S204000

Reexamination Certificate

active

06498068

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to methods of producing resistor elements of a layered structure which may be used as a chip-type thermistor or a chip-type resistor element. More particularly, this invention relates to method of producing such resistor elements having mutually oppositely facing pairs of inner electrodes inside a resistor base body.
It has been known to use chip-type thermistor elements as a temperature-sensitive element or an element for temperature compensation. Elements of this type having different resistance values are frequently required, depending on where they are used. In response to such a requirement, chip-type thermistor elements of different structures have been proposed. Japanese Utility Model Publication Jikkai 6-34201 and Japanese Patent Publication Tokkai 4-130702 have disclosed various kinds of chip-type thermistor elements using a sintered ceramic body obtained by sintering together a ceramic material with inner electrodes.
FIGS. 10 and 11
show, as an illustration, the structure of a prior art thermistor element
151
of such a layered structure having a sintered ceramic base body
152
comprising a semiconductor ceramic material with a negative temperature coefficient. Mutually opposite end surfaces of this sintered ceramic body are referred to, for convenience, as the first end surface
152
a
and the second end surface
152
b.
Outer electrodes
159
and
160
are formed so as to cover the first and second end surfaces
152
a
and
153
b,
respectively. A set of horizontally extending inner electrodes (referred to as the first electrodes)
153
,
154
and
155
are formed at different heights inside the sintered ceramic body
152
so as to be exposed to the exterior on the first end surface
152
a.
Correspondingly, another set of horizontally extending inner electrodes (referred to as the second electrodes)
156
,
157
and
158
are formed respectively at the heights of the first electrodes
153
,
154
and
155
inside the sintered ceramic body
152
so as to be exposed to the exterior on the second end surface
152
b,
the electrodes
153
and
156
forming a pair, the electrodes
154
and
157
forming another pair, and the electrodes
155
and
158
forming still another pair. Each pair of first and second electrode is in a coplanar relationship and separated by a gap of a same specified width and is designed such that the gaps between these three pairs of inner electrodes overlap in the vertical direction, that is, the direction of the thickness of the sintered ceramic body
152
.
The resistance of the thermistor element
151
thus structured is adjustable to a desired value by varying the size of the gap between the aforementioned first and second inner electrodes as well as the number of pairs of first and second inner electrodes. In order to accurately set the resistance value of the thermistor element
151
, therefore, it is necessary not only to highly accurately set the gap between the first and second inner electrodes of each pair but also to form each inner electrode
153
-
158
such that the gaps therebetween are all accurately positioned in the direction of the thickness of the sintered ceramic body
152
. In other words, strict process management was indispensable for the production of chip-type thermistor elements having a desired resistance value.
When chip-type thermistor elements having different resistance values are desired, either the gap between the first inner electrodes
153
-
155
and the second inner electrodes
156
-
158
or the number of layered pairs of inner electrodes must be changed. If the width of the gaps is to be changed, however, a different electrode pattern must be prepared and printed on ceramic green sheets with a conductive paste in order to obtain sintered ceramic bodies by the conventional integral sintering technology. Since the accuracy involved in the printing of conductive paste cannot be improved beyond a certain limit, variations in the resistance values of the thermistor elements thus obtained are significantly large, and the center of distribution of these resistance values tends to be significantly far away from the desired value. In other words, the yield of acceptable products is not sufficiently high, if it is desired to produce resistor elements with resistance values having only small variations.
Because the gap size and the accuracy in overlapping layers must be strictly controlled if a desired resistance value is to be accurately attained, as explained above, it becomes very expensive to produce chip-type thermistors with many different resistance values. Problems of this kind have been in existence not only with thermistor elements but also with varistors and fixed resistors with a similar inner electrode structure.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a method of producing resistor elements having mutually oppositely facing pairs of inner electrodes in a layered structure with different resistance values by using only a small number of inner electrode patterns.
It is another object of this invention to provide methods of producing such resistor elements.
A resistor element according to a first embodiment of the invention, by which the above and other objects can be accomplished, may be characterized as comprising a ceramic body having a first end surface and a second end surface which are facing away from each other, a first outer electrode on the first end surface and a second outer electrode on the second end surface and a plurality of mutually oppositely facing pairs of inner electrodes inside the ceramic body. Each of these pairs has a first inner electrode extending horizontally from the first end surface towards the second end surface and a second inner electrode extending horizontally from the second end surface towards the first end surface and having a front end opposite and separated from the first inner electrode by a gap of a specified width, these plurality of pairs forming layers in a vertical direction. The gap of at least one of these plurality of pairs of inner electrodes is horizontally displaced from but overlapping with the gaps between the other pairs of inner electrodes. Such a resistor element is produced according to this invention by first setting a distance of displacement according to a target resistance value intended to be had by the resistor elements and then displacing the gap of at least one of the plurality of pairs of inner electrodes horizontally by this distance of displacement.
Resistor elements according to a second embodiment of the invention are similar to those according to the first embodiment of the invention except the thickness of those portions of the ceramic body between at least one of mutually adjacent pairs of the inner electrodes is different from the thickness of the portions of the ceramic body between the other mutually adjacent pairs of the inner electrodes. Such a resistor element can be produced by first obtaining a layered structure by vertically stacking a plurality of mutually oppositely facing pairs of horizontally extending inner electrodes each consisting of a first electrode and a second electrode having oppositely facing front parts with selected numbers of ceramic green sheets inserted between mutually vertically adjacent pairs of the inner electrodes, the selected numbers being determined according to a target resistance value intended to be had by the resistor element, then subjecting the layered structure to a firing process to thereby obtain a resistor body having a first end surface and a second end surface which face away from each other, and next forming a first outer electrode on the first end surface and a second outer electrode on the second end surface.
Resistor elements according to this invention are advantageous not only because their resistance values can be finely adjusted by simple steps but also because those having different resistance values can be manufactured with a small number of patterns for printing electrode patterns on

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