JPS61114139A - Differential pressure sensor - Google Patents

Abstract

PURPOSE:To improve sensitivity by joining the 2nd diaphragm which has the same material with the 1st diaphragm to the side of the 1st diaphragm where a hole is formed. CONSTITUTION:The part of the n<+> diffused layer 2b in the 1st hole 3 is etched in a rod shape and a P layer as a substrate is under-etched to form the 2nd hole 5, thereby forming an oscillation beam 4 of the n<+> layer. Then, a P<+> layer 6 is formed by diffusion or epitaxial growth at the part which is most sensitive to the oscillation of the oscillation beam 4. This P<+> layer is led out through an unshown lead wire, etc., while insulated from the P layer to form p-n junction on the oscillation beam 4 as the n<+> diffused layer. The 2nd diaphragm and the 2nd diaphragm are anode-joined together under a vacuum to produce a vacuum in the 1st hole and the 2nd hole. Thus, differential pressure is dealt with and the sensitivity is improved.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention relates to a differential pressure sensor that outputs a force corresponding to a differential pressure generated across a diaphragm as a frequency signal, and uses a semiconductor substrate such as silicon to eliminate this The present invention relates to a differential pressure sensor having a structure in which a vibrating beam is formed on a plate.

<Conventional example> Measured pressure is received by a diaphragm, and the force generated on the diaphragm is detected by a strain gauge installed on the diaphragm.
Differential pressure sensors that convert into electrical signals are well known and have already been widely put into practical use.

In such a differential pressure sensor, the strain gauge exhibits an analog resistance value change according to the force to be measured, and its output value is also small. For this reason, when the output signal is processed by a computer or the like, it is not necessary to amplify or perform A/D conversion.

A differential pressure sensor that obtains a frequency signal corresponding to differential pressure is also available.
This is known, for example, as seen in Japanese Unexamined Patent Publication No. 54-56880. This device applies a force generated on a diaphragm to a vibrating wire coupled to the diaphragm, and obtains a change in the natural frequency related to the tension of the vibrating wire as a frequency signal output.

In this device, it is necessary to connect the two so that the force generated in the diaphragm can be accurately transmitted to the vibration line, and a configuration must be devised so that changes in the environment around the vibration line will not cause changes in the natural frequency of the vibration line. There was a problem that the configuration became complicated due to the necessity of

<Objective of the Invention> The present invention has been made in view of the problems of the prior art described above, and an object of the present invention is to provide a differential pressure sensor with a simple configuration that outputs a frequency signal corresponding to a differential pressure.

<Configuration of the Invention> The configuration of the present invention that achieves this object is to form holes in the surface of the first diaphragm made of an elastic semiconductor material, one of which is closed and the other of which is open, by etching and underedging techniques. A vibration beam having both ends fixed is provided in the middle of this hole, and a second diaphragm made of the same material as the first diaphragm is joined to the side of the first diaphragm having the hole, and the vibration beam is fixed at both ends. Kirinari's feature is that the hole is evacuated and the diaphragm of M1 is equipped with an excitation means for a vibrating beam and a vibration detection means.

<Example> Fig. 1 is a perspective view showing the overall configuration of a differential pressure sensor V according to the present invention, and Fig. 2 shows a main part of the differential pressure sensor shown in Fig. 1 (portion A surrounded by a chain line). It is a cross-sectional enlarged perspective view. In these figures, 1 is the diaphragm of ff11,
For example, it is a p-type silicon substrate with an impurity concentration of 1015 or less. On the surface of this silicon substrate 1, 0+ diffusion layers 2a, 2b, and 2c of approximately the impurity depth g1io+e are formed, and the first holes 3 are formed by partially etching these diffusion layers to a predetermined thickness. do. Next, the part of the n+ diffusion layer 2b in the first hole 3 is etched into a rod shape, and the p layer that is the substrate is under-etched to form a second hole 5, and the vibrating beam 4 made of the n middle layer is etched. form. Reference numeral 6 denotes a p-middle layer formed by diffusion or epitaxial growth in the part where the vibration of the vibrating beam 4 is most felt (both ends of the beam in the figure). This p10 layer 6 is insulated from the 0 layer 1 which is the substrate and taken out to the outside by a lead wire (not shown) or the like, and forms a pO junction on the vibrating beam 4 which is the n0 diffusion layer. 7 is a second diaphragm made of the same material as the first diaphragm, and the second diaphragm and the first diaphragm are anodically bonded in a vacuum, so that the first hole and the second hole are kept in a vacuum state. becomes. 8 is a 5tO2 film, for example, which functions as a bonding agent and an insulating agent.

In the above configuration, if the thicknesses of the first diaphragm 1 and the second diaphragm 7 are made approximately equal, the bonding surface becomes the neutral plane, so the stress generated in the diaphragm is minimized at the neutral plane, and the stress generated by the bonding is minimized at the neutral plane. The impact can be reduced to almost zero. Moreover, the withstand pressure against static pressure in the part where the vibrating beam 4 is formed is determined by making the ratio 14/13 of the width of the hole 2ρ and the thickness of the diaphragm membrane 1!4 sufficiently large (not shown in FIG. 3). It can be solved. For example, 13-
3 μm, 1a = 3 μm, and the maximum stress of silicon is 10
When kO/1111', the breakdown voltage PO is Po-<14
/j'3)2-crmax-"IQQOk<1/el
l”.

On the other hand, distortion due to static pressure in the axial direction of the beam can be ignored by making 13/R (R is the radius of the diaphragm, see FIG. 1) sufficiently small.

Note that these processes can be performed using photolithography technology.

The differential pressure sensor configured as described above is fixed by a fixing means (not shown), and pressure is applied from both sides of the diaphragm. and,
A negative bias is applied to the p layer, which is the first diaphragm, and a vibration distortion signal due to distortion of the diaphragm is detected from a pn junction formed at the end of the vibrating beam. When this strain signal is amplified and fed back positively to the first diaphragm 1, the vibrating beam is excited at its natural frequency by electrostatic force.

This vibration changes according to the differential pressure applied to the diaphragm, resulting in a distorted feeling r! I S is given by the following formula.

S-Δf/f o =0.118・<1+/l2)2
-ε (ε is strain) This change in the vibration frequency of the vibrating beam 4 due to strain is a well-known 1! not shown in the figure. Detected by first detection means.

According to the device configured in this way, the vibration beam is formed in the pressure receiving diaphragm in a vacuum state, so that the ideal
It is possible to reduce single bullet retention by 1q, and to realize a stable monolithic sensor with a high Q.

In the above embodiment, the first diaphragm was made of a p-type silicon substrate, but this substrate was made of an n-type, and this n-type silicon substrate was used as the first diaphragm.
A p-type beam may be formed by diffusing a p-layer on a shaped substrate, and a diode for vibration detection may be formed on the p-type beam. Also,
The number of vibrating beams is not limited to one; for example, if another vibrating beam is formed in the center of the diaphragm, sensitivity can be doubled and thermal distortion caused by temperature changes can be canceled.

Furthermore, the shape of the diaphragm can be other than circular.

<Effects of the Invention> As described above in detail with the embodiments, according to the present invention, a stable frequency signal with a high Q can be outputted in response to differential pressure, and the structure is simple. A differential pressure sensor can be realized.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing the overall configuration of a differential pressure sensor according to the present invention, Fig. 2 is an enlarged cross-sectional perspective view showing main parts of the differential pressure sensor shown in Fig. 1, and Fig. 3 is a diaphragm in a beam forming part. FIG. DESCRIPTION OF SYMBOLS 1... First diaphragm, 2a-2C... Diffusion layer, 3.5... Hole, 4... Vibration beam, 7... Second diaphragm.

Claims (1)

[Claims] A hole is formed on the surface of the first diaphragm made of an elastic semiconductor material by etching and under-etching, one of which is closed and the other is open, and a vibrating beam with both ends fixed is provided in the middle of this hole. A second diaphragm made of the same material as the first diaphragm is bonded to the side of the first diaphragm that has the hole, and the hole is evacuated to excite a vibrating beam provided on the first diaphragm. A differential pressure sensor characterized by comprising a means for detecting vibration and a means for detecting vibration.