阅读说明：本技术 一种高灵敏度微型皮拉尼计 (High-sensitivity miniature Pirani gauge ) 是由 韩建强 任杨波 徐好 于 2020-06-17 设计创作，主要内容包括：本发明公开了一种基于正、负电阻温度系数的高灵敏度微型皮拉尼计的结构及制作方法,属于微电子机械系统领域。其结构特征在于微型皮拉尼计采用两个正电阻温度系数加热器(1)作为惠斯通全桥电路一对对边,两个负电阻温度系数加热器(2)作为另一对对边。微型皮拉尼计工作时,在惠斯通电桥的一对对边加载恒定直流电压,正电阻温度系数加热器(1)和负电阻温度系数加热器(2)温度升高,阻值分别增加和下降。腔体内真空度不同,阻值变化量不同,从惠斯通电桥另一对角输出的电压也相应发生改变,通过测量惠斯通电桥的输出电压可反映出封装腔体内的真空度。本发明所涉及的微型皮拉尼计有以下优点：测量灵敏度高,可检测的最小压力和漏率低。(The invention discloses a structure and a manufacturing method of a high-sensitivity micro Pirani gauge based on positive and negative resistance temperature coefficients, and belongs to the field of micro-electro-mechanical systems. The micro Pirani gauge is structurally characterized in that two positive resistance temperature coefficient heaters (1) are used as one pair of opposite sides of a Wheatstone full-bridge circuit, and two negative resistance temperature coefficient heaters (2) are used as the other pair of opposite sides. When the micro Pirani gauge works, constant direct current voltage is loaded on a pair of opposite sides of the Wheatstone bridge, the temperature of the positive resistance temperature coefficient heater (1) and the temperature of the negative resistance temperature coefficient heater (2) are increased, and the resistance values are respectively increased and decreased. The vacuum degree in the cavity is different, and the resistance variation is different, and the voltage of following another diagonal output of wheatstone bridge also changes correspondingly, can reflect the vacuum degree in the encapsulation cavity through measuring wheatstone bridge's output voltage. The micro Pirani gauge has the following advantages: the measuring sensitivity is high, and the detectable minimum pressure and the leak rate are low.)

1. A high-sensitivity miniature Pirani gauge is characterized in that: the device comprises two positive resistance temperature coefficient heaters (1), two negative resistance temperature coefficient heaters (2), a structural layer (3), a passivation layer (4), a lead (5), a bonding pad (6) and a substrate (7), wherein the positive resistance temperature coefficient heaters (1) and the negative resistance temperature coefficient heaters (2) are positioned between the structural layer (3) and the passivation layer (4) and suspended on the substrate (7); an air gap exists between the structural layer (3) and the substrate (7), and the passivation layer (4) is positioned on the positive resistance temperature coefficient heater (1), the negative resistance temperature coefficient heater (2) and the structural layer (3).

2. The high sensitivity micro pirani meter of claim 1, wherein: the two positive resistance temperature coefficient heaters (1) are used as a pair of opposite sides of the Wheatstone full-bridge circuit, and the two negative resistance temperature coefficient heaters (2) are used as the other pair of opposite sides of the Wheatstone full-bridge circuit; when the micro Pirani gauge works, constant direct current voltage is loaded on a pair of opposite angles of a Wheatstone bridge, current flows through a positive resistance temperature coefficient resistor (1) and a negative resistance temperature coefficient resistor (2), the temperatures of the positive resistance temperature coefficient resistor (1) and the negative resistance temperature coefficient resistor (2) are increased, the resistance value of the positive resistance temperature coefficient resistor (1) is increased, and the resistance value of the negative resistance temperature coefficient resistor (2) is reduced; when the vacuum degree in the cavity changes, the convection heat exchange quantity changes along with the change, the resistance values of the positive resistance temperature coefficient resistor (1) and the negative resistance temperature coefficient resistor (2) change, and the vacuum degree in the packaging cavity can be reflected by measuring the output voltage of the Wheatstone bridge.

3. The high sensitivity micro pirani meter of claim 1, wherein: the method is prepared by the following basic process steps:

1) the original material is a silicon wafer;

2) manufacturing a sacrificial layer (8) on the surface of the silicon wafer;

3) manufacturing a structural layer (3);

4) manufacturing a positive resistance temperature coefficient heater (1) on the structural layer (3);

5) manufacturing a negative resistance temperature coefficient heater (2) on the structural layer (3);

6) sputtering, photoetching and corrosion processes are combined to manufacture a lead (5) and a metal bonding pad (6);

7) depositing a passivation layer (4), and exposing the metal pad (6) by combining photoetching and etching processes;

8) the photoetching and etching process are combined to manufacture a corrosion window (9);

9) corroding the sacrificial layer (8), releasing the structural layer (3), the passivation layer (4) and the positive resistance temperature coefficient heater (1) and the negative resistance temperature coefficient heater (2) which are manufactured on the passivation layer;

10) scribing;

11) and packaging, welding leads, connecting with an external circuit, taking the two positive resistance temperature coefficient heaters (1) as a pair of opposite side bridge arms of the Wheatstone bridge, and taking the two negative resistance temperature coefficient heaters (2) as the other pair of opposite side bridge arms of the Wheatstone bridge.

Technical Field

The invention relates to a Micro Pirani gauge, in particular to a structure of a high-sensitivity Micro Pirani gauge based on positive and negative resistance temperature coefficients and a manufacturing method thereof, belonging to the field of Micro-Electro-mechanical systems (MEMS).

Background

Many MEMS devices need vacuum packaging to work normally, such as micro gyroscopes, micro accelerometers, and micro biomolecular mass detectors based on resonant structures. The vacuum packaging can reduce the damping of gas when the mechanical moving part moves, thereby obtaining higher quality factor and sensitivity. The devices such as uncooled infrared detection and imaging instruments, flow meters, micro chromatographs and the like based on the heat conduction principle need vacuum packaging to prolong the molecular mean free path of free particles, so that the sensitivity of the devices is improved. Vacuum packaging techniques are key techniques that affect the performance parameters of these MEMS devices.

The conventional MEMS device vacuum degree detection method mainly comprises a helium leak detector, a resonator Q value detection method and a micro Pirani gauge. The helium leak detector is very high in price and low in test precision, and can not perform real-time online detection on vacuum degree change inside the cavity. The Q value detection method is characterized in that the Q value of an MEMS resonator in a vacuum packaging body is measured, the vacuum degree in a packaging cavity is reversely deduced by using a formula, but the measurement error is large under high vacuum, and the resonance frequency of the resonator is drifted by the relaxation of the stress of a film material forming the micro-resonator.

The operating principle of the Pirani gauge is as follows: the heat generating object is related to the convective heat transfer of the ambient air and the gas pressure in the cavity. When the gas pressure changes, the convective heat transfer between the heating object and the surrounding air will be different. Compared with the traditional filament-based Pirani gauge, the miniature Pirani gauge has the advantages of small volume, low power, quick thermal response, wide pressure measurement range and the like. Compared with a resonator, the micro pirani meter has higher detection sensitivity.

In order to raise the upper limit of the detection pressure range, the distance between the heater and the radiator should be minimized. To lower the lower dynamic range limit, the micro pirani gauge should have a large surface area and the heater should have a high temperature coefficient of resistance. The heater is made of platinum, nickel and polysilicon, and the temperature coefficient of resistance of the heater is positive. The heater is used as one arm of the Wheatstone bridge or a group of opposite sides of the Wheatstone bridge, and the sensitivity of the micro Pirani meter is difficult to be further improved due to the limitation of the resistance temperature coefficient of the thin film material.

Disclosure of Invention

The invention aims to invent a high-sensitivity micro Pirani gauge to detect the vacuum degree in a vacuum packaging cavity.

In order to realize the purpose of the invention, the adopted technical scheme is as follows: the micro Pirani gauge comprises two positive resistance temperature coefficient heaters (1), two negative resistance temperature coefficient heaters (2), a structural layer (3), a passivation layer (4), a lead (5), a bonding pad (6) and a substrate (7). The positive resistance temperature coefficient heater (1) and the negative resistance temperature coefficient heater (2) are manufactured on the upper surface of the structural layer (3). The structural layer (3) is suspended above the substrate (7), an air gap exists between the structural layer and the substrate, and heat of the positive resistance temperature coefficient heater (1) and the negative resistance temperature coefficient heater (2) is conducted to the substrate (7) serving as a heat radiator through gas thermal convection in the air gap. The passivation layer (4) is deposited on the upper surfaces of the positive resistance temperature coefficient heater (1), the negative resistance temperature coefficient heater (2) and the structural layer (3) to prevent the positive resistance temperature coefficient heater (1), the negative resistance temperature coefficient heater (2) and the lead (5) from being corroded or oxidized.

The invention relates to a detection mechanism of a high-sensitivity micro Pirani meter, which comprises the following steps: the two positive resistance temperature coefficient resistors (1) and the two negative resistance temperature coefficient resistors (2) form a Wheatstone bridge, wherein the two positive resistance temperature coefficient resistors (1) are used as a pair of opposite side bridge arms of the Wheatstone bridge, and the two negative resistance temperature coefficient resistors (2) are used as the other pair of opposite side bridge arms. When the micro Pirani gauge works, constant direct current voltage is loaded on a pair of opposite angles of a Wheatstone bridge, and current flows through a positive resistance temperature coefficient resistor (1) and a negative resistance temperature coefficient resistor (2). The positive resistance temperature coefficient resistor (1) and the negative resistance temperature coefficient resistor (2) are increased in temperature. The resistance value of the positive resistance temperature coefficient resistor (1) is increased, and the resistance value of the negative resistance temperature coefficient resistor (2) is reduced. When the vacuum degree in the cavity changes, the convection heat exchange quantity changes along with the change of the vacuum degree, the resistance values of the positive resistance temperature coefficient resistor (1) and the negative resistance temperature coefficient resistor (2) change, and the output voltage of the other pair of opposite angles of the Wheatstone bridge also correspondingly changes. The output voltage of the Wheatstone bridge is measured to reflect the vacuum degree in the packaging cavity.

The invention relates to a high-sensitivity micro Pirani gauge based on positive and negative resistance temperature coefficients, which is manufactured by the following basic process steps:

1) the starting material is a silicon wafer.

2) And manufacturing a sacrificial layer (8) on the surface of the silicon wafer.

3) And manufacturing a structural layer (3).

4) And manufacturing a positive resistance temperature coefficient heater (1) on the structural layer (3).

5) And manufacturing a negative resistance temperature coefficient heater (2) on the structural layer (3).

6) And (3) combining sputtering, photoetching and corrosion processes to manufacture the lead (5) and the metal pad (6).

7) A passivation layer (4) is deposited, and the metal pad (6) is exposed by combining photoetching and etching processes.

8) And (3) combining photoetching and etching processes to manufacture a corrosion window (9).

9) And corroding the sacrificial layer (8), releasing the structural layer (3), the passivation layer (4), and the positive resistance temperature coefficient heater (1) and the negative resistance temperature coefficient heater (2) which are manufactured on the passivation layer.

10) And (6) scribing.

11) And packaging, welding leads, connecting with an external circuit, taking the two positive resistance temperature coefficient heaters (1) as a pair of opposite side bridge arms of the Wheatstone bridge, and taking the two negative resistance temperature coefficient heaters (2) as the other pair of opposite side bridge arms of the Wheatstone bridge.

The invention relates to a micro Pirani gauge structure based on positive and negative resistance temperature coefficients and a manufacturing method thereof, which has the advantages that: the device has higher measurement sensitivity, and can detect smaller pressure and leakage rate in the vacuum chamber.

Drawings

FIG. 1 is a schematic structural diagram of a high-sensitivity micro Pirani gauge based on positive and negative resistance temperature coefficients according to the invention.

FIG. 2 is a flow chart of the manufacturing process of the high sensitivity micro Pirani gauge based on positive and negative temperature coefficient of resistance along the view angle AA' in FIG. 1.

FIG. 3 is a schematic diagram of a Wheatstone bridge of the high-sensitivity micro Pirani meter based on positive and negative temperature coefficients of resistance according to the present invention.

In the drawings:

1-positive resistance temperature coefficient heater 2-negative resistance temperature coefficient heater 3-structural layer

4-passivation layer 5-lead 6-pad

7-substrate 8-sacrificial layer 9-etch window

Detailed Description

The invention is further illustrated, but not limited, by the following example 1 in conjunction with figure 2.