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Pressure sensor classification

Material Type Output
element
Displace-
ment base material
Package
Ni,Cu
alloy
Resistantwire
type
Strain
gauge
Sheet of
polyimide,
etc.
bare
SUS
Semi
conductor
Si
Diffusion
type
Strain
gauge
Si
diaphragm
CAN
Plastic
SUS
Deposition
type
Strain
gauge
SUS
diaphragm
SUS
Capacitance
type
Al film Si
diaphragm
Plastic
Ceramic Capacitance
type
Metal film Alumina
diaphragm
SUS
Others Mechanical Brass plate
Light receiving
element
Spring Many kinds

The pressure sensors have a lot of types, and on a material basis they are classified as shown in the table 1. The sensor made from the semiconductor Si has 10 times higher sensitivity than the resistant-wire type using the alloy of Ni and Cu. Among all types, the diffusion type made by applying the micromachining technology has the high productivity, and this type is manufactured most because it has the following features. - The relative pressure (= gauge pressure) type covers the wide range of 2kPa to 20MPa - The absolute pressure type can be also produced On the other hand, the deposition type using the SUS diaphragm is suitable for the high pressure use, and the capacitance type using parallel pates is suitable for the very small pressure use. In addition, the diffusion type and the capacitance type are also applied to the integrated sensor. As for packages, CAN is mainly used for automobile, plastic is for public, and SUS case is for high pressure/ food.


Pressure sensor usage

半導体圧力センサ

As shown in the table 2, the pressure sensors are used in a lot of fields, for instance, the hot-water supply machine, air-conditioner, air-pressure-meter, blood pressure machine, and EFI(Electronic Fuel Injection), etc.

Public use hot-water supply machine, air-conditioner, cloth washer,
dish washer, vacuum, etc.
FA use air-pressure-meter, water-pressure-meter, oil-pressure-meter, etc.
Automobile
use
Electronic Fuel Injection (fuel pressure, intake pressure, air pressure)
Others blood pressure machine, differential pressure gauge, etc.

Principle of diffusition type pressure sensor operation

Principle of diffusition type pressure sensor operation

As shown in the plan of figure 1, in a case of the pressure sensor chips, gauges like strip of paper are formed by impurity diffusion at 4 points, and in the same direction. And after connecting the Si, processed to diaphragm as shown in the cross section, on the glass plinth, the sensor is formed into chip. After assembling this sensor chip into each type of cases, when pressed from the glass plinth side, gauges A and C are transformed as shown in the pattern diagram X, and those resistance increase. In addition, gauges B and D are transformed as shown in Y, and those resistance decrease. Practicably, as shown in the connection diagram, the gauges are connected with Wheatstone bridges, the voltage difference between the terminals plus and minus is used as output. Adversely, when pressed from the Si side, increase and decrease of gauge resistance will become contrary, according to it, plus and minus of the output is also reversed. In the chips, there are two types. One is connected with Wheatstone bridges on the surface of Si, and another is terminal No. 1 and 6 are opened to make it easy to adjust the offset voltage from the externals.

Pressure sensor structure

Pressure sensor structure

The figure 2 shows the cross section structure of the case type of semiconductor pressure sensor for gauge pressure.

Characteristics of pressure sensors

Characteristics of pressure sensors

Actually, a lot of characteristics are required to the pressure
sensors as follows.
1. Bridge resistance
2. Offset voltage (output voltage at 0kPa)
3. Output span voltage (Output voltage - Offset voltage)
4. Linearity (difference between the output at half of the
rated pressure and the calculated value )
5. Pressure hysteresis (difference when set at the rated
pressure and turn it back to 0kpa again)
6. Destruction resisting pressure (is opposite to the output
span voltage)
7. Temperature characteristic
8. Various reliabilities
As a main characteristic, following shows the output span
voltage (figure 3) and the destruction resisting pressure histogram
(figure 4) of our products


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