JPS62145780A - Semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To provide a semiconductor pressure sensor which has adaptability for a living body such as insulation and antithrombus and accelerates a pressure responding speed by covering the optimum surface of a portion capable of making contact with atmosphere to be measured including at least diaphragm portion with a thin diamond film. CONSTITUTION:An N-type silicon single crystal is used as a substrate, a diaphragm 2 is provided on a sensor chip body 1, four piezo resistors 3 which become 2kOMEGA at 35 deg.C are formed on the diaphragm, are electrically connected via diffused leads 4 as a bridge, only this portion is not covered to execute inputs/outputs by aluminum pads 5, and the other entire surface is covered with a thin diamond film 6. Thus, a semiconductor pressure sensor to be used as a catheter end type blood pressure sensor has adaptability for a living body equivalent to or more than the conventional technique, excellent pressure sensitivity and remarkably excellent responding speed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor pressure sensor that utilizes the piezoresistance effect of a semiconductor, and particularly to an ultra-small semiconductor pressure sensor that can be mounted at the tip of a catheter.

BACKGROUND OF THE INVENTION In recent years, the demand for pressure sensors has rapidly increased in fields such as (a) medical use, (b) automobile use, and (C) industrial measurement use. A silicon diaphragm pressure sensor that utilizes the piezoresistive effect is attracting attention as the only one that can meet these requirements. The reason for this is due to the following many advantages or possibilities. In other words, ■Mass production possible, ■Low price, ■High precision,
■High reliability, ■Small and lightweight, ■Multi-functionality, etc.

Among these, the ones that have recently attracted particular attention are (a) catheter-tip blood pressure sensors that utilize small size and light weight for medical purposes; This is intended to be inserted into the body of a critically ill patient such as an ICU (intensive care unit) to accurately measure blood pressure at local sites within the heart or blood vessels.

↓ Fig. 8 shows an example of a catheter tip type blood pressure sensor. (a) is a cross-sectional structural diagram thereof, and (b) is a schematic plan view.

Such catheters are extremely long and thin with a diameter of approximately 1.0 to 2.4 mm, and have a silicon diaphragm-type pressure sensor chip (1) fixed on a ceramic substrate (7) and a diaphragm (2) as a pressure-sensitive part. ) is applied with the blood pressure to be measured from the upper part, and the lower part is opened to atmospheric pressure from the air hole (6) through a conduction tube made of nylon or the like. Electrically, the metal pad on the chip (1) is connected to the metal wiring (8) on the ceramic substrate through the bonding wire (9), and is further connected to the external monitor through the soldered lead wire (b). . In addition, parts that are likely to be damaged by cutting, such as bonding wires, are reinforced with hard resin 0Q1, such as epoxy resin, and other parts are reinforced with soft resin (0Q1) to ensure appropriate softness.
g) For example, the edges are formed on urethane resin. Furthermore, there is a hole called a lumen used for blood collection and measurement of cardiac output, etc., and an attached tube/dout made of polyethylene, etc., including the top of the diaphragm part (2) of the sensor chip (1). The outer wall of the catheter is coated with urethane resin.

The surface of the semiconductor pressure sensor chip itself used in such catheter-tip blood pressure sensors is generally coated with S to prevent the entry of ions from body fluids and ensure insulation.
It is covered with a passivation film such as an i02 film or a SiN film. Since these films are frequently used in the manufacture of normal semiconductor integrated circuits, their formation technology is almost established and mass production is possible.

However, when these membranes come into direct contact with blood, blood coagulation occurs on the membrane surface (hereinafter referred to as thrombus), which is dangerous, so they are not coated with medical silicone rubber or urethane resin as shown in Figure 3. This coating technology is not an established technology and it is difficult to control the absolute value and uniformity of the coating thickness.

6 However, the material of the coating film is too soft;
3. If the tube is too thick, the response speed to pressure fluctuations will be significantly slow, and the distortion of the blood pressure waveform due to the compliance of the tube and the inertia and viscosity of the blood, which was solved by using a catheter tip type, is different from the distortion of the blood pressure waveform. The blood pressure waveform will be distorted, and the advantages of the catheter tip type will not be fully utilized.

Purpose of the Invention The present invention has biocompatibility such as insulation and antithrombotic properties to the extent that it can be mounted on the tip of a catheter and used for direct measurement of blood pressure, etc. in vivo, and has a pressure response speed. The purpose of this paper is to propose a sufficiently fast semiconductor pressure sensor structure.

Means for Solving the Problems In the present invention, since it is not possible to add antithrombotic properties to the semiconductor pressure sensor chip body as in the prior art, antithrombotic properties are acquired by coating with a resin etc. that cannot be mass-produced. Rather, it has achieved both biocompatibility and pressure response speed by acquiring antithrombotic properties through a method that can be incorporated into the semiconductor integrated circuit manufacturing technology that enables highly precise microfabrication used in sensor manufacturing.

That is, a diamond thin film is used as a material to obtain antithrombotic properties. This diamond thin film can be formed using a hydrocarbon gas such as CHa, C2H8, C5Hs, C4H10, etc. by a thin film forming technique that is common in semiconductor integrated circuit manufacturing technology, such as plasma CVD, and although it cannot be said to be a perfect diamond crystal, it is almost have equal characteristics. The antithrombotic properties are much better than silicone rubber or glass, and are almost the same as segmented polyurethane (which has excellent antithrombotic properties and has a reputation as a medical material). Also, regarding insulation, 1
It has a resistivity of 0' to 1014 Ω, which is equal to or higher than a 5in2 film or a SiN film used for passivation of semiconductor integrated circuits.

From the viewpoint of processability, it is possible to form almost uniformly at a rate of 1,500 to 2,000 X/H with a temperature rise of at most 100°C, and it can be etched with O2 plasma, making it possible to reduce the cost of photolithography. In the same way that semiconductor integrated circuits can be manufactured inexpensively and in large quantities, semiconductor pressure sensors with high biocompatibility and quick pressure response can be manufactured stably and easily.

Effects and Examples The present invention will be described below based on specific examples.

FIG. 1 is a diagram showing the structure of a semiconductor pressure sensor in which the surface of the sensor chip is coated with a diamond thin film, which is an embodiment of the present invention, (a) is a surface configuration diagram of the sensor chip, (b)
The figure is a sectional view including the diaphragm part in the longitudinal direction of the sensor chip, and the same figure (c) is a sectional view including the diaphragm part in the direction orthogonal to this.

In this example, an n-type silicon single crystal is used as the substrate,
1.5 x 4. Omm size and thickness 0.4 mm
A diaphragm (2) with a size of 0.5 x 1.5 mm and a thickness of 15 μm is provided on the sensor chip body (1), and a piezoresistor (3) that has a resistance of 2 to Ω at 35°C is attached to the diaphragm (2). As can be done through individual diamonds, only this part is left uncovered and the entire other surface is covered with a diamond thin film (
6). The thickness of this sharp diamond thin film is 3000A.

FIG. 2 shows the structure of a blood pressure sensor in which this semiconductor pressure sensor is attached to the tip of a catheter. (a) The figure is a cross-sectional view,
(b) is a schematic plan view.

This is achieved by a third method using a semiconductor pressure sensor according to the prior art.
Compared to the blood pressure sensor shown in the figure, there is only one difference. That is, the presence or absence of a resin coating on the surface of the sensor chip to obtain antithrombotic properties. This resin coating is performed with a thickness of 200 μm as a tentative goal, but in reality there is no method to accurately measure the coating thickness, and the coating thickness varies greatly between sensors and is not uniform.

A comparison of the characteristics of these two types of sensors is as follows.

However, the standard data such as sensitivity is 9,0OO on Figure 1.
The CVD-5ioz film of A is formed as a passivation film, on which a diamond thin film is formed in the sensor according to the present invention, and coated with resin in the sensor according to the prior art.

(1) Output sensitivity = 0 to 300mmHg with 1v constant voltage drive
In the range of
g, whereas that of the present invention was the same as the reference value.

(it) Insulation: Almost the same as measured by leakage current after being immersed in water for 8 hours.

(1■) Antithrombotic properties: Equivalent in in vitro evaluation using human blood.

(iφ response speed: Since there is no standard pressure generator with a clear response speed, a quantitative comparison cannot be made, but the output profile when changing the pressure in a stepwise manner is sharper in the one by Akira Kito, and In the conventional technology, there are variations between cefsa.

Effects of the Invention To summarize the effects of the present invention, a semiconductor pressure sensor that can be used as a catheter tip-type blood pressure sensor has biocompatibility equivalent to or better than that of the conventional technology, slightly better pressure sensitivity, and overwhelmingly superior Not only can it have a high response speed, but it can also be manufactured in large quantities with dramatically small variations.

As a result, catheter-tip blood pressure sensors can be made more accurate and less expensive, and it is expected that they will become more widespread.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a semiconductor pressure sensor in which the surface of the sensor chip is coated with a diamond thin film, which is an embodiment of the present invention, (a) is a surface configuration diagram of the sensor chip, (b)
The figure is a sectional view including the diaphragm part in the longitudinal direction of the sensor chip, and the same figure (c) is a sectional view including the diaphragm part in the direction perpendicular to this. FIG. 2 is a diagram showing the structure of a blood pressure sensor in which a semiconductor pressure sensor according to the present invention is attached, and FIG. 3 is a diagram showing the structure of a blood pressure sensor in which a semiconductor pressure sensor according to the prior art is attached to the tip of a catheter.
The figure is a sectional view, and the figure (b) is a schematic plan view. 1. Sensor chip body 2, diaphragm part 8, piezoresistor 4, diffusion lead part lO-5, AA pad 6, diamond thin film 7, ceramic substrate 8, metal wiring 9, bonding wire 10, hard resin 11, Lead wire 12, air hole 13, atmospheric pressure transmission tube 14, lumen tube 15, lumen 16, soft resin 17, catheter outer wall

Claims (1)

[Claims] In a semiconductor pressure sensor in which a diaphragm part is formed on a semiconductor substrate, and a piezoresistive part as a pressure receiving element is formed on the diaphragm part, the outermost surface of the part including at least the diaphragm part that may come into contact with the atmosphere to be measured is A semiconductor pressure sensor characterized by being coated with a diamond thin film.