CN108387341A - Miniature vacuum gauge and working method thereof - Google Patents

Abstract

The invention discloses a miniature vacuum gauge and its working method. The miniature vacuum gauge comprises a base, a frame, an insulating base, a diode, a resistor, a cantilever beam and electrical connection wires, the frame is fixed around the base, and there are at least two cantilever beams. One end of the cantilever beam is fixedly connected to the insulating base, the other end of the cantilever beam is fixed on the upper side of the frame, and at least two cantilever beams suspend and fix the insulating base on the frame; the diode and the resistor are arranged on the insulating base, and the electrical connection wires The resistor and the diode are electrically connected and drawn out from the cantilever beam. The invention realizes accurate detection of different vacuum degrees by configuring the number of diodes, the series-parallel connection mode of the diodes, the size of the series resistance, and the gap between the insulating base and the base, and has the advantages of flexible configuration, high sensitivity and large measuring range. In addition, the vacuum gauge also has the advantages of simple structure and manufacturing method, compatibility with CMOS technology, large processing error tolerance, low cost and the like.

Description

Miniature Vacuum Gauge and Its Working Method

technical field

The invention relates to a miniature vacuum gauge and its working method.

Background technique

A vacuum gauge is an instrument used to measure gases below one atmospheric pressure. Generally, the air pressure is measured by using the change of a certain physical effect of the gas under different air pressures, and it is widely used in scientific research and industrial production. After more than 300 years of development, there are many types of vacuum gauges today, such as liquid vacuum gauges, capacitive film vacuum gauges, resonant vacuum gauges, heat conduction vacuum gauges, and ionization vacuum gauges. At the same time, the measurement range and measurement accuracy are greatly improved.

MEMS is developed on the basis of microelectronics technology, which is a high-tech electromechanical device made by combining technologies such as lithography, corrosion, thin film, silicon micromachining, non-silicon micromachining and precision machining. MEMS is a revolutionary new technology widely used in high-tech industries. It focuses on ultra-precision machining and involves many disciplines such as microelectronics, materials, mechanics, chemistry, and mechanics.

Instruments such as micro accelerometers and micro gyroscopes made by microfabrication technology have been widely used in recent years. The maintenance of the vacuum degree in the microsystem vacuum packaging largely determines the final performance, reliability and life of the device, and the monitoring of the vacuum degree in the package is an important research field in vacuum packaging.

Pirani vacuum gauge is also called resistance vacuum gauge, which is a kind of heat conduction vacuum gauge. Its working principle is: the number of air molecules per unit volume is different when the degree of vacuum is different, and the heat dissipation capacity of the resistance wire is different accordingly, which is manifested as the temperature of the resistance wire is different, because the resistivity of the resistance wire is a function of temperature, then it is different The vacuum degree will cause the resistivity of the resistance wire to be different, which will cause the resistance to be different, and the voltage drop on the resistance wire will be different. The Pirani gauge is a vacuum degree detection device with high precision, relatively simple manufacturing process and testing. The miniature Pirani gauge made by bulk silicon processing technology has the advantages of small size, high measurement accuracy, easy mass production, and low cost, and is widely used in real-time vacuum measurement of MEMS vacuum packaging.

On March 11, 2008, Peking University filed a patent application with publication number CN101256105A titled "Single Crystal Silicon Transverse Micro MEMS Pirani Meter and Its Preparation Method", disclosing a micro Pirani meter for vacuum degree measurement. meter; on June 9, 2009, Huazhong University of Science and Technology filed a patent application for a Pirani meter manufacturing method with the publication number CN101608962A and the name "a miniature Pirani meter", which has good linearity, stable performance, and chemical stability. Good and high reliability advantages. On March 19, 2014, Peking University proposed a patent application for a Pirani meter manufacturing method with the publication number CN104931193A and the name "A MEMS Pirani meter with a reference vacuum chamber", which can effectively eliminate the environmental temperature. The reading error of the Pirani gauge. On September 12, 2014, Huazhong University of Science and Technology proposed the preparation and integration method of the Pirani meter with the publication number CN104340955A and the name "Preparation method of micro-Pirani meter and its integrated processing method with bulk silicon devices". Patent application can reduce the difficulty of integrated packaging process and production cost.

At present, the commonly used methods for detecting vacuum degree of MEMS devices mainly include: inert gas He value detection method, resonator Q value detection method, thin film deformation method and Pirani meter. These methods have more or less certain problems. Among them, the He value detection method requires very precise detection instruments, resulting in high cost and low precision, and it cannot monitor the vacuum degree in real time; the Q value detection method mainly detects vacuum packaging. The Q value of the MEMS device is reversed by the formula, the peripheral circuit is complex, and it is greatly affected by external interference; the existence of the thin film deformation method limits the application range; the Pirani gauge is a kind of heat conduction vacuum gauge, The detection of the vacuum degree is realized by using the characteristics of the thermistor, which effectively reduces the production cost while maintaining the detection accuracy. However, the Pirani meter usually needs to be matched with peripheral circuits in practical applications; in the actual processing process, there are large processing errors in the resistance, and it is difficult to process resistance with large resistance.

Contents of the invention

In order to overcome the above-mentioned defects, the present invention provides a miniature vacuum gauge and its working method, which uses the temperature characteristic of the current-voltage characteristic curve of the diode to realize the change of the output electric signal of the diode, thereby realizing the detection of the vacuum degree.

The technical solution adopted by the present invention in order to solve the technical problems is: a miniature vacuum gauge, including a base, a frame, an insulating substrate, a diode, a resistor, a cantilever beam and electrical connections, the frame is fixed around the base, and the There are at least two cantilever beams, one end of the cantilever beam is fixedly connected to the insulating base, the other end of the cantilever beam is fixed on the upper side of the frame, at least two cantilever beams connect the insulating The base is suspended and fixed on the frame; the diode and the resistor are arranged on the insulating base, and the electrical connection wire electrically connects the resistor and the diode and leads out from the cantilever beam.

As a further improvement of the present invention, the base is a silicon, quartz or glass substrate.

As a further improvement of the present invention, the frame is an insulating structure.

As a further improvement of the present invention, the diode is a PN junction.

As a further improvement of the present invention, there are multiple diodes, and the multiple diodes are connected in series or in parallel.

As a further improvement of the present invention, the resistor is one or more of polysilicon, metal resistors and parasitic resistors produced by processing, and is connected in series with the diode.

As a further improvement of the present invention, the cantilever beam is an insulating beam.

As a further improvement of the present invention, the cantilever beam is L-shaped.

As a further improvement of the present invention, the electrical connection is made of polysilicon, metal or multiple materials, and placed in the cantilever beam.

The present invention also provides a working method of the miniature vacuum gauge as described above. If the diode works under a constant bias current, the miniature vacuum gauge measures the voltage between the two ends of the diode and the degree of vacuum through an electrical connection. relationship to obtain vacuum degree information; if the diode works under a constant bias voltage, the micro vacuum gauge measures the relationship between the diode current and vacuum degree through an electrical connection to obtain vacuum degree information.

The beneficial effects of the present invention are:

1. There is a junction voltage in the PN junction diode, and the working voltage can be quickly increased or lowered by configuring the number of series diodes to adapt to the working voltage of common CMOS circuits, without the need for large resistance resistors and sophisticated conditioning circuits;

2. The processing and manufacturing of PN junction can allow a large processing error tolerance, and the product performance consistency is good;

3. The working current under normal working conditions is small, and the power consumption is effectively reduced without losing the working voltage;

4. The structure and processing steps are simple, effectively reducing production costs;

5. By configuring the number of diodes and series-parallel connection, the size and number of resistors, the thickness of the sacrificial layer and the size of the bias current, the sensitivity and range of the vacuum gauge can be flexibly changed.

Description of drawings

Fig. 1a is a schematic structural diagram of a vacuum gauge according to an embodiment of the present invention;

Fig. 1b is a schematic diagram of an exploded structure of a vacuum gauge according to an embodiment of the present invention;

Fig. 2a, 2b, 2c, 2d, 2e, 2f are a kind of process flow diagram of manufacturing steps of the vacuum gauge described in the embodiment of the present invention, wherein: Fig. 2a is the step of growing silicon dioxide, and Fig. 2b is the P-type implantation in the sensitive structure region Steps; Figure 2c is the N-type injection step of the diode; Figure 2d is the step of making the electrical connection; Figure 2e is the step of patterning the cantilever beam and the insulating substrate; Figure 2f is a schematic diagram of the step of completing the suspension structure.

In conjunction with the accompanying drawings, the following descriptions are made:

1. Base, 2. Frame, 3. Insulating substrate, 4. Diode, 5. Resistor, 6. Cantilever beam, 7. Electrical wiring, 21. Bulk silicon, 22. Silicon dioxide, 23. Deposited silicon, 24 . Polysilicon or metal.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Apparently, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

FIG. 1 is a structural schematic view of the miniature vacuum gauge of the present invention, which comprises: a base 1, a frame 2, an insulating substrate 3, a diode 4, a resistor 5, a cantilever beam 6 and an electrical connection 7. The frame 2 is fixed around the base 1; the insulating base 3 is located above the base 1 and has a gap with it, and is connected to the frame 2 through a suspended cantilever beam 6; the diode 4 and the resistor 5 are arranged on the insulating base 3; the electrical connection 7 It is electrically connected with the diode 4 and the resistor 5, and is located on the cantilever beam 6.

The base 1 is a silicon, quartz or glass substrate, which is used to provide base support for the vacuum gauge, and the complete structure of the vacuum gauge is located on the base. In order to reduce processing steps and reduce manufacturing difficulty, silicon is preferably used as the base material.

The frame 2 is an insulating structure that provides support for the three-dimensional structure of the vacuum gauge. The frame 2 is located outside the entire vacuum gauge structure and directly determines the size of the vacuum gauge; the frame 2 part does not require any electrical connection. Generally, the material of the frame 2 of the vacuum gauge can be: silicon oxide, silicon nitride, etc., and silicon oxide is the preferred material.

The diode 4 is a PN junction, and the current-voltage characteristic curve of the diode 4 shifts to the left as the temperature of the diode increases, and different degrees of vacuum will cause different temperatures on the diode. As a result, the current-voltage characteristics of the diode 4 change to detect the degree of vacuum.

The diode 4 can be one or multiple; multiple diodes 4 are connected in series or in parallel. Under constant bias current, connecting multiple diodes in series can improve the detection sensitivity, connecting multiple diodes in parallel can increase the heat source power, and using both in series and parallel can improve the detection sensitivity while increasing the heat source power.

The resistor 5 is a specially made polysilicon resistor or metal resistor, or it may be a parasitic resistor generated during processing. There can be one or more resistors, which are connected in series with the diodes. The function of the resistance is to provide an additional heat source for the vacuum gauge, which affects the temperature of the diode 4, and the auxiliary diode 4 detects the degree of vacuum.

The cantilever beam 6 is an insulating beam, and its shape can be an "L" beam, a folded herringbone or other shapes of the cantilever beam. The cantilever beam 6 connects the insulating base 3 and the frame 2 to provide support for the suspended insulating base 3 . At the same time, the cantilever beam 6 provides a lead-out path for the electrical connection, and the electrical connection is made on the cantilever beam 6, and the cantilever beam 6 itself has no requirement for electrical connection.

The electrical connection 7 is polysilicon, metal connection or connection made of multiple materials. The electrical connection 7 connects the electrical signal of the vacuum gauge to the outside through the path provided by the cantilever beam 6 . In particular, metal Al is used as the electrical connection material.

In order to improve the detection sensitivity of the present invention to the degree of vacuum, a simple and feasible method is to increase the number of diodes 4 . The connection modes of the diode 4 include: series connection, parallel connection, and mixed series and parallel connection. Connecting diodes in series can increase the sensitivity of detection, connecting diodes in parallel can increase the power of diodes as a heat source, and using a combination of series and parallel connections can increase the power of heat sources and improve detection sensitivity at the same time. The specific number of diodes used and the connection method need to be designed according to the range and accuracy requirements of the vacuum degree to be measured.

A kind of typical processing step of realizing the present invention comprises:

1), growing a sacrificial layer on the front side of the polished silicon substrate;

2), depositing silicon on the grown sacrificial layer;

3), making diodes and resistors on the deposited silicon;

4), Graphical cantilever beams to complete the electrical connection production;

5), corrode and release the sacrificial layer, and complete the manufacture of the vacuum gauge.

By controlling the thickness of the sacrificial layer, the gap between the diode and the base after the sacrificial layer is released can be controlled, thereby affecting the range and sensitivity of the vacuum gauge. The material of the sacrificial layer can be silicon dioxide, polyimide, BCB, polysilicon, amorphous silicon or bulk silicon etc. The silicon deposited on the sacrificial layer is used as an insulating base, and a diode is fabricated on the insulating base as a sensitive structural layer. The diode itself is used as a core sensitive unit and also as a heat source. The resistance fabricated on the insulating substrate acts as a heat source, which can be a specially fabricated resistance or a parasitic resistance during processing. Resistors can be ordinary resistors or thermistors. When using a common resistor, it is only used as a heat source; when using a thermistor, it can help improve the sensitivity of the vacuum gauge. Generally, there is no need to design a special resistor. The material of the cantilever beam structure can be silicon, silicon dioxide, silicon nitride, Ti, Al, Au and other metals. The electrical connection can be made of metal, polysilicon or multiple materials.

The preparation process of the miniature vacuum gauge of this embodiment using ordinary silicon wafers includes the following steps:

Growing silicon dioxide 22 on the front side of the polished silicon substrate 21, as shown in Figure 2a;

Deposit silicon 3 on the silicon dioxide, and perform P-type implantation in the sensitive structure area at the same time, as shown in Figure 2b;

Perform N-type implantation on the deposited silicon 23, anneal to form a diode, and complete the diode fabrication, as shown in FIG. 2c;

Perform heavy doping on the silicon at the cantilever beam as the connecting lead of the diode, or deposit metal 24 to realize the extraction of electrical signals at both ends of the diode, as shown in Figure 2d;

Patterning cantilever beams and diode sensitive structures, as shown in Figure 2e;

Etching releases the silicon dioxide 22 of the sacrificial layer to complete the fabrication of the vacuum gauge, as shown in FIG. 2f.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims (10)

1. a miniature vacuum gauge, is characterized in that: comprise base (1), frame (2), insulating substrate (3), diode (4), resistance (5), cantilever beam (6) and electric wire (7) ), the frame is fixed around the base, there are at least two cantilever beams, one end of the cantilever beam is fixedly connected to the insulating base, and the other end of the cantilever beam is fixed on the upper side of the frame above, at least two of the cantilever beams suspend and fix the insulating base on the frame; the diode and the resistor are arranged on the insulating base, and the electrical connection wire electrically connects the resistor and the diode and derived from the cantilever beam. 2. The miniature vacuum gauge according to claim 1, characterized in that: the base is a silicon, quartz or glass substrate. 3. The miniature vacuum gauge according to claim 1, characterized in that: the frame is an insulating structure. 4. The miniature vacuum gauge according to claim 1, characterized in that: the diode is a PN junction. 5. The miniature vacuum gauge according to claim 4, characterized in that: there are multiple diodes, and the multiple diodes are connected in series or in parallel. 6. The miniature vacuum gauge according to claim 1, wherein the resistor is one or more of polysilicon, metal resistor and parasitic resistor produced by processing, and is connected in series with the diode. 7. The miniature vacuum gauge according to claim 1, characterized in that: the cantilever beam is an insulating beam. 8. The miniature vacuum gauge according to claim 7, characterized in that: the cantilever beam is L-shaped. 9. The miniature vacuum gauge according to claim 1, characterized in that: the electrical connection is made of polysilicon, metal or multiple materials, and placed in the cantilever beam. 10. A working method of the miniature vacuum gauge according to any one of claims 1 to 9, characterized in that: if the diode works under a constant bias current, the miniature vacuum gauge is electrically connected Measure the relationship between the voltage across the diode and the degree of vacuum to obtain information about the degree of vacuum; if the diode is working at a constant bias voltage, the miniature vacuum gauge will measure the relationship between the diode current and the degree of vacuum through an electrical connection , to obtain vacuum degree information.