JPS61181171A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To miniaturize a semiconductor pressure sensor while improving sensitivity by forming the plane shape of a diaphragm to a shape long in the specific direction apart from a true circle and an equilateral polygon. CONSTITUTION:The shape of a diaphragm formed at the centerl section of a sensor chip is formed to a shaped as an ellipse and a rectangle long in the direction that the size of a chip leaves a margin, not an equilateral polygon. When a central symmetrical shape such as the ellipse and the rectangle is formed even when the diaphragm having a shape long in the specific direction is formed, there is a region in which the linearity of stress generated by the deformation of the diaphragm is kept excellent. The peripheries of the major axis and the minor axis in the ellipse and the periphery, etc. of two linear symmetrical axes in the rectangle correspond to the region. Accordingly, since the diaphragm is lengthened just a bit in the direction having allowance, the quantity of defor- mation to the fixed pressure of the diaphragm is increased, thus augmenting stress generated in the direction, then improving the sensitivity of pressure.

Description

Detailed Description of the Invention (a) Technical field to which the invention pertains The present invention utilizes the piezoresistance effect of semiconductors to
The present invention relates to a semiconductor pressure sensor that measures fluid pressure such as water pressure.

(b) Prior art and its problems Semiconductor pressure sensors using silicon as a material are attracting attention because of the availability of recent highly developed semiconductor highly integrated circuit manufacturing technology and its mechanical strength. This is achieved by providing a thin diaphragm of approximately 5 to 30 μm in the center of a silicon single crystal substrate, forming a diffused piezoresistor as a pressure-sensitive element on this diaphragm, and using the piezoresistance effect to control pressure from changes in resistance. It is detected by converting it into a voltage change.

The schematic structure of this example is shown in FIG. In the figure, n
A diaphragm (2) with a thickness of 10 μm is provided at the center of the - type silicon single crystal substrate (1), and p-type diffused piezoresistors (3, 4, 5
, 6) are formed. These p-type diffused piezoresistors (3, 4, 5, 6) are connected to the p-type diffused lead part (7
) to the Al terminals (8, 9, 10, 11>).By assembling four p-type diffused piezoresistors into a bridge circuit in this way, pressure sensitivity is improved.Actually A constant current or constant voltage is applied between the AA terminal (8) (terminal 1) and the M terminal α0 (terminal 3), and the AJ
Detect voltage changes at the j terminal (9) (terminal 2) and the A/terminal aυ (terminal 4).

The greatest advantage of such a semiconductor pressure sensor is that it can be easily combined with a signal processing circuit and can be miniaturized by making full use of semiconductor highly integrated circuit manufacturing technology. For this reason, it has become possible to consider applications that would not be easily realized using metal resistance strain gauges. A typical example is when it is attached to the tip or side of a catheter.
This is a catheter-type pressure sensor that is inserted into a blood vessel to directly monitor I/ζ blood pressure values in vivo. For such pressure sensors to be mounted on the tip or side of the catheter,
The width of the sensor chip must be made as small as possible,
It must be kept to about 1.5M at maximum. In this case, the problem is that the maximum dimension of the diaphragm that can be formed in the center of the chip is naturally determined by the sensor chip size restriction. In other words, the most important factor that determines the sensitivity of a pressure sensor is the ratio of the diaphragm size to the diaphragm portion, but if you want to obtain high sensitivity when the diaphragm size cannot be increased, the diaphragm portion must be made thinner. However, it is difficult to realize a highly sensitive pressure sensor because the diaphragm part also has limitations due to problems such as processing technology and pressure resistance limits.

(c) Purpose of the Invention The purpose of the present invention is to propose a structure for a semiconductor pressure sensor that can be miniaturized to the extent that it can be attached to the tip of a catheter, etc., and still make it relatively easy to realize a highly sensitive sensor. do.

B) Means for Solving the Problems The semiconductor pressure sensor according to the present invention has a diaphragm formed in the center of the sensor chip that is not shaped like a regular polygon such as a perfect circle, square, or regular hexagon as conventionally used. The main feature is that the chip is shaped like an ellipse or rectangle, which is longer in the direction that allows for the chip dimensions.

The direction of miniaturization desired for semiconductor pressure sensors differs depending on the field of application. For example, in the case of a catheter-type pressure sensor, the diameter of the catheter is about &5- or less, so the diametrical tip size is at most 2.0
Although it must be kept to about 10 mm, it is permissible up to about 10 am in the axial direction of the catheter. In this case, the semiconductor pressure sensor of the present invention is constructed by creating a sensor chip that is long in the axial direction and forming an elliptical or rectangular diaphragm that is long in that direction.

The diaphragm of conventional semiconductor pressure sensors has a shape with poor directionality, such as a perfect circle, a square, or a regular polygon such as a regular hexagon. This was done to increase the degree of freedom in the formation position and shape of the piezoresistor by making it as small as possible over the entire surface.

On the other hand, even if a diaphragm is formed with a long shape in a specific direction as in the present invention, if the shape is centrally symmetrical such as an ellipse or a rectangle, the linearity of the stress caused by the deformation of the diaphragm is well maintained. A region exists. For example, the areas around the long axis and short axis of an ellipse, and the areas around two axes of line symmetry in a rectangle.

Now, the biggest advantage of the present invention is that by making the diaphragm as long as possible in a direction with a margin, the amount of deformation of the diaphragm with respect to a constant pressure increases, which in turn increases the stress generated in that direction, which reduces pressure sensitivity. It's about getting bigger.

(e) Examples The present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram showing the structure of a silicon diaphragm type pressure sensor as an embodiment of the present invention.

(a) of the figure is a surface configuration diagram of the sensor chip, (b) is a cross-sectional view including the diaphragm part in the longitudinal direction of the sensor chip, (
c) is a sectional view including the diaphragm portion in a direction perpendicular to this. In the figure, the substrate is 1.5 mm x 40
mm n-type silicon single crystal substrate (1) with a thickness of 0
．． It is 4 pieces, the surface is (100) and the side is (110).
It is a surface. The diaphragm (2) with a thickness of 10/jm was etched from the back side with an alkaline etching solution such as a mixture of ethylenediamine, pyrocatechol, and water to form a diaphragm (2) with a size of 0.5 wr x 1.5 am. A rectangular shape is formed, and a p-type diffused viezo resistor (3, 4, 5
゜6) are perpendicularly intersecting at the center of the short side (3:R1 and 5:Rs), and the p+ Four Al terminals (8) are connected via the mold diffusion lid part (7).
, 9, 10, 11) and detect pressure using exactly the same input and output.

In this case, the two p-type diffused piezoresistors (R1, Rs) formed perpendicularly to the sides of the rectangular diaphragm receive stress in the direction along the resistor due to pressure from the top of the diaphragm, which increases the resistance value. On the contrary, the soil is left behind. The positions where these four p-type diffused piezoresistors are formed are regions where the stress is highly linear.

(F) Effects of the Invention As mentioned above, by using the structure of the semiconductor pressure sensor of the present invention, it is possible to relatively easily realize a highly sensitive sensor even if it is miniaturized to the extent that it can be attached to the tip of a catheter, etc. become.

Brief explanation of the front screen Figure 1 is a diagram showing the structure of a silicon diaphragm type pressure sensor having a rectangular diaphragm, which is an embodiment of the present invention, and Figure 2 is a diagram showing the structure of a silicon diaphragm type pressure sensor having a square diaphragm according to the prior art. FIG. 3 is a diagram showing the structure of a silicon diaphragm type pressure sensor. In each figure, (a) is a surface configuration diagram of the sensor chip, (b) is a cross-sectional view including the diaphragm part in the longitudinal direction of the sensor chip, and (c) is a cross-sectional view including the diaphragm part in the direction orthogonal to this. It is.

In-type silicon single crystal substrate 2 Diaphragm 3p-type diffused piezoresistor (R1) 4 (Rg) 5　　　　　　　(Rs)〃 6 (R4) 7p 10 type diffusion lead part 8 A7 terminal (terminal l)

Claims (1)

[Claims] (1) In a semiconductor pressure sensor in which a diaphragm that deforms depending on the atmosphere to be measured is provided in the center of a semiconductor crystal plate, and a diffused resistor as a pressure-sensitive element is formed in the diaphragm portion, the planar shape of the diaphragm is a perfect circle. A semiconductor pressure sensor that differs from a regular polygon in that it has a long shape in a specific direction.