JPH0138377B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor variable resistance element that facilitates analog signal multiplication processing, that is, signal modulation, demodulation, frequency conversion, etc.

Conventionally, bipolar transistors or field effect transistors have been used as semiconductor variable resistance elements used to process analog signals. These have characteristics that the impedance between the collector and emitter or the impedance between the drain and source changes depending on the base current or the voltage between the gate and source, and are generally used for variable attenuators, frequency converters, etc. has been done.

However, the size of the variable impedance (in this case, the impedance between the collector and emitter or the impedance between the drain and source),
There is no relationship between the magnitude of the control signal (in this case, the base current or the voltage between the gate and the source) that can be established by a simple relational expression, and the device is inappropriate as an element that performs analog signal multiplication processing.

FIG. 1 is for conceptually explaining the characteristics that a variable resistance element that can be applied to analog signal multiplication processing should have.

In FIG. 1, variable resistance element 1 is controlled by control voltage Vc or control current Ic applied from terminal 2.
It is assumed that the resistance value R is controlled. This variable resistance element 1 is supplied with another signal voltage by a signal source 3.
Since Vs is applied, the current flowing through the variable resistance element 1 is expressed as Is (Vs/R). Here and now,
If the resistance value R of the variable resistance element 1 is inversely proportional to the control voltage Vc or the control current Ic, the above-mentioned current Is is proportional to the product of Vs and Vc or Vs and Ic.

As described above, the present invention aims to obtain a variable resistance element whose resistance value is inversely proportional to the magnitude of a control signal.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a top plan view of an element when the present invention is applied to a bipolar IC process, that is, a so-called composite mask drawing, and FIG. 3 is a cross-sectional view taken along the line A-A' shown in FIG. The figure is shown below.

In Figure 2, 4 is the N-type emitter diffusion layer (emitter region), 5 is the P-type base diffusion layer (base region), 6 is the N-type collector epitaxial layer (collector region), and 7 is the P-type isolation layer. A diffusion layer or a dielectric isolation layer is shown, and 10 is an aluminum wiring layer. Further, reference numeral 8 indicates a window portion formed in an oxide insulator 9 provided on the semiconductor surface for connecting the semiconductor portion and the aluminum wiring portion 10.

Furthermore, E, B, and Co represent emitter, base, and collector electrodes, respectively, and C _R1 and _CR2 represent resistance element electrodes when used as a variable resistance element.

On the other hand, FIG. 3 is a sectional view taken along line A-A' shown in FIG. 2.

Next, the operating principle of the present invention will be explained using FIG. 3.

In the present invention, as in a normal bipolar transistor, the carrier concentration (impurity concentration) in the emitter region 4 is made much higher than that in the base region 5, and by applying a forward bias voltage between the emitter and the base, the emitter A minority carrier proportional to the emitter current is injected into the base region 5 immediately below. This injected minority carrier mainly diffuses downward towards the collector-base junction and reaches the collector region 6 via this junction if the collector junction is zero-biased or reverse-biased. Now, just like a normal bipolar transistor, the emitter just below the emitter,
If the distance between the base bonding surface, the collector directly below the bonding surface, and the base bonding surface, the so-called base width, is kept sufficiently shorter than the diffusion length of the minority carrier injected into the base, the base region 5 will be smaller than the emitter region 4. The minority carriers injected into the base region 5 reach the collector region 6 without almost disappearing in the base region 5.

In this way, the carriers that reach the collector area become the majority carriers in the collector area, and
Increases the electrical conductivity of the collector region directly below the base-collector interface.

Now, in a normal bipolar process, if the carrier concentration (impurity concentration) in the collector region formed by the epitaxial layer is made low enough, the electrical conductivity of the collector region directly below the base and collector junction surface will be lower than that of the emitter. It will vary approximately in proportion to the majority carrier provided through the emitter current, i.e. in proportion to the emitter current.

The present invention changes the electrical conductivity of the collector region immediately below the base-collector junction surface in proportion to the emitter current, that is, the resistance value of the region is inversely proportional to the emitter current. The objective is to obtain a variable resistance element whose resistance is inversely proportional to a control signal.

In order to achieve this objective, it is necessary to eliminate as much as possible the various parasitic elements that occur when realizing a variable resistance element.

The pattern arrangement shown in FIG. 2 is an example of a pattern arrangement obtained by taking the above parasitic elements into consideration.

In other words, as parasitic elements that are undesirable to occur in FIG. 2, the resistance element electrodes C _R1 and C _R2
Then, there is a resistance section formed in the collector diffusion region 6 which is not covered by the base region 5, and this resistance section is arranged in parallel with the variable resistance section formed in the collector region directly under the base region.

In addition, the resistance section from the collector region directly under the base region to the resistance element electrodes _CR1 and _CR2 is also desirable and is a parasitic element, and this resistance section is a variable resistance section formed in the collector region directly below the base region. and enter in series.

Some specific means for avoiding the influence of these parasitic elements as much as possible will be explained below. In other words, the parasitic resistance elements that are connected in series are patterned so that their resistance values are as small as possible, and the carrier concentration (impurity concentration) of the collector region around the resistance element electrodes _CR1 and _CR2 is adjusted. It is effective to add a collector-all process to thicken the
In addition, for parasitic resistance elements that are connected in parallel, in order to increase the resistance value as much as possible, the width of the collector region that is not covered by the base region is made as short as possible, and the length of the collector region is made as long as possible. It becomes effective.

In addition, resistive element electrodes C _R1 and C _R2 are placed in the collector area.
The reason for providing a separate collector electrode Co is that the emitter current, which is a control signal, is connected to this collector electrode Co.
is removed to the outside through the resistive element electrode C _R1 ,
This is to prevent the control signal from having an adverse effect on C _R2 , and it is desirable to arrange the electrode Co at a position symmetrical to the electrodes C _R1 and C _R2 , as shown in the figure.

In the same sense, it is of course preferable that the base electrode B is placed at a position symmetrical to the electrodes C _R1 and C _R2 .

As described in detail above, according to the present invention, it is possible to easily obtain a variable resistance element whose resistance value changes in inverse proportion to a control signal by using a conventional bipolar IC process. It can be applied to processing, and its practical effects are extremely large.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram for conceptually explaining the characteristics of a variable resistance element that can be applied to analog signal multiplication processing, FIG. 2 is a plan view of a semiconductor variable resistance element according to an embodiment of the present invention, and FIG. The figure is a sectional view taken along line A-A' in FIG. 2. 4... Emitter area, 5... Base area, 6...
... Collector region, 7 ... P-type isolation diffusion layer and substrate or dielectric separation layer, 9 ... Oxide insulating layer, 10 ... Aluminum wiring layer, E ... Emitter electrode, B ... Base electrode, Co ... ...Collector electrode,
C _R1 , C _R2 ...Electrodes for resistance elements.

Claims (1)

[Claims] 1. An N-type (or P-type) semiconductor region with a high carrier concentration (impurity concentration) forming an emitter region, and a low carrier concentration (impurity concentration) forming a base region in contact with the emitter region. It consists of a P-type (or N-type) semiconductor part and an N-type (or P-type) semiconductor part with a low carrier concentration (impurity concentration) that contacts this base region to form a collector region, and from the emitter region to the base region. The base width is made sufficiently narrow so that the injected minority carriers reach the collector region without almost disappearing, and the collector region is expanded to both sides of the portion in contact with the base region. The collector region is provided with two resistance electrodes for using the portion of the collector region directly below the emitter that is in contact with the base region as a resistance element, and the collector region is further provided with two resistance electrodes for use as a resistance element. The electrode is expanded in a direction different from the direction in which it is expanded to form the electrode, a collector electrode is provided in this portion, and a base electrode and an emitter electrode are provided in the base region and emitter region, respectively. Semiconductor variable resistance element. 2 The carrier concentration (impurity concentration) of the collector region extending on both sides of the collector region in contact with the base region is calculated as the carrier concentration (impurity concentration) of the collector region in contact with the base region.
The semiconductor variable resistance element according to claim 1, characterized in that the semiconductor variable resistance element is made darker. 3 Apply forward bias between the emitter electrode and base electrode, apply zero bias or reverse bias between the base electrode and collector electrode, change the forward bias applied between the emitter and base, or change the emitter current. The carrier injected from the emitter region into the base region reaches the collector region via the base region, and by varying the conductivity of the collector region in contact with the base region, the resistance value between the two resistor electrodes is changed. 2. The semiconductor variable resistance element according to claim 1, wherein the semiconductor variable resistance element is made variable.