CN105527042B

CN105527042B - Pressure sensor and method for manufacturing the same

Info

Publication number: CN105527042B
Application number: CN201510666874.5A
Authority: CN
Inventors: 汤姆·科瓦
Original assignee: Zhejiang Dunan Artificial Environment Co Ltd
Current assignee: Zhejiang Dunan Artificial Environment Co Ltd
Priority date: 2014-10-15
Filing date: 2015-10-15
Publication date: 2020-06-05
Anticipated expiration: 2035-10-15
Also published as: CN105527042A

Abstract

The invention discloses a pressure sensor assembly, comprising: three stacked silicon wafers forming a support, a sensor, and a lid, wherein the sensor comprises a cavity extending upward from a bottom of the sensor toward a top of the sensor to form a cavity bottom and a diaphragm; a dielectric layer covering the bottom of the sensor and the cavity, and wherein the support is coupled to the dielectric layer along the bottom of the sensor; a plurality of ports on the top of the support within the defined area of the cavity, the plurality of ports extending through the support to the bottom thereof, and wherein the cover is coupled to the top of the sensor, covering the diaphragm; and a second cavity cut into the bottom of the lid, wherein the second cavity is sized and positioned to surround the diaphragm.

Description

Pressure sensor and method for manufacturing the same

Technical Field

The invention relates to a pressure sensor and a manufacturing method thereof. More particularly, the present invention relates to pressure sensors made from silicon wafers.

Background

Existing designs for high pressure backside applications of pressure sensors are inadequate for many applications. A typical pressure sensor uses a diaphragm as a pressure detection element of the pressure sensor. The diaphragm is exposed to positive or negative pressure on only one side, creating a pressure differential across the diaphragm. The pressure differential causes the diaphragm to flex by an amount that can cause a change in, for example, resistance or capacitance, which can be measured by a circuit.

One problem with existing designs is that they do not restrict the pressure flow to the diaphragm. Thus, when the pressure sensor is exposed to a drastic change, the diaphragm will experience a very rapid pressure change. Such rapid pressure changes may cause the diaphragm to bend beyond its yield point and permanently damage the diaphragm and, ultimately, the pressure sensor.

Another problem with existing designs is that the silicon diaphragm is directly exposed to the medium whose pressure needs to be measured. The impact of the high potential conductive fluid on the silicon surface will cause large currents to flow through the sensor and cause damage to the sensor and/or the circuitry attached thereto.

Yet another problem with existing designs is that there is no detection means when the diaphragm has reached its displacement limit. Since such detection means may impair the displacement limit state.

Disclosure of Invention

In view of the above, according to one aspect of the present invention, it is an object to provide a pressure sensor assembly. Preferably, these methods and apparatus solve or at least ameliorate one or more of the problems described above. To this end, a pressure sensor assembly is provided. In one embodiment, the pressure sensor assembly comprises: a first silicon wafer having a top and a bottom; a cavity formed within the silicon die, the cavity extending upward from a bottom of the first silicon die toward a top of the first silicon die forming a cavity bottom such that a diaphragm is formed between the cavity bottom and the first silicon die; a dielectric layer covering the bottom of the first silicon wafer and the cavity; a conductive layer, such as a metal (e.g., aluminum), or heavily doped polysilicon, covering the top of the diaphragm within the first silicon wafer; a second silicon die coupled to the dielectric layer along a bottom of the first silicon die and covering the cavity; a plurality of ports located in an area defined by the cavity at the top of the second die, the plurality of ports extending through the second die to the bottom of the second die; a third silicon die coupled to the top of the first silicon die such that the third silicon die covers the diaphragm; and a second cavity cut into the bottom of the third silicon die, wherein the second cavity is sized and positioned such that the second cavity surrounds the diaphragm.

In a preferred embodiment, the depth of the second cavity is designed to mechanically limit the displacement of the diaphragm to less than 3 times the full range pressure displacement. In a preferred embodiment, the depth of the second cavity is less than or equal to 0.9 μm.

In still other embodiments, the second cavity may also include means for electronically detecting that the diaphragm has reached its displacement limit. In such embodiments, a conductive layer may cover the bottom of the cavity or be suitably placed on the bottom of the cavity. A respective conductive layer may cover or be suitably placed on the top of the membrane. Thus, when the diaphragm reaches its maximum displacement, the conductive layer on the top of the diaphragm and the conductive layer on the bottom of the second cavity are in contact. The layers may be designed, sized and shaped such that the contact between the layers completes the circuit, thus electronically detecting that maximum displacement of the diaphragm has occurred. In some embodiments, the conductive layer in the bottom of the second cavity may be in electrical communication with contacts on another region of the sensor assembly. In a preferred embodiment, the contacts may be located on top of the third silicon die. The conductive layer may be made of a metal such as aluminum or heavily doped polysilicon.

In some embodiments, the bottom of the cavity forming the diaphragm is located at 80% of the distance to the top of the first silicon wafer. In other embodiments, other depths may be used.

In a preferred embodiment, the dielectric layer insulates the circuitry on the sensor from the media impacting the diaphragm. In a preferred embodiment, the dielectric layer insulates the circuitry on the sensor from the support. In a preferred embodiment, the dielectric layer is made of silicon dioxide or silicon nitride or a combination of silicon dioxide and silicon nitride. In some embodiments, the first silicon die is directly coupled to the second silicon die without using a dielectric layer.

In some embodiments, the pressure sensor assembly may be further coupled to a substrate. In such embodiments, the substrate may be coupled to the bottom of the second silicon die. The substrate may include a channel extending from a top of the substrate to a bottom of the substrate. The openings of the channels at the top of the substrate may encompass the openings of the plurality of ports at the bottom of the second silicon wafer. In some embodiments, the substrate may be a susceptor.

Other embodiments of the pressure sensor are also described. In one embodiment, the pressure sensor assembly comprises: a first silicon wafer having top and bottom surfaces and an intermediate plane defined at an intermediate location between the top and bottom surfaces, wherein the bottom surface includes a cavity extending upwardly toward the top surface through which a cavity bottom is formed; a diaphragm formed between the bottom of the cavity and the top surface; a second silicon die coupled to the bottom surface of the first silicon die, the second silicon die covering the cavity to form a chamber; a plurality of channels extending through the second silicon wafer and into the chamber; a third silicon die coupled to the top surface of the first silicon die, the third silicon die comprising a second cavity sized and positioned to cover the diaphragm, and wherein a bottom of the second cavity forms a mechanical stop for the diaphragm; and wherein the first and second silicon wafers are electrically insulated from each other by a dielectric layer located therebetween.

In a preferred embodiment, the bottom of the second cavity may be covered with a conductive layer positioned to close an electrical circuit if pressure applied to the diaphragm causes the conductive layer on top of the diaphragm to contact the conductive layer on the bottom of the second cavity.

According to another aspect of the present invention, a method of manufacturing a pressure sensor assembly is provided. In a preferred embodiment, the method comprises: forming a sensor from the first silicon wafer by forming a cavity extending from a bottom up into the first silicon wafer; forming a conductive layer on top of the first silicon wafer; forming a dielectric layer on the bottom of the first silicon chip and the cavity; forming a support from a second silicon wafer by forming a plurality of channels, wherein the plurality of channels pass through the second silicon wafer from a top surface to a bottom surface; bonding the bottom of the first silicon wafer to the top surface of the second silicon wafer such that a chamber is formed by the cavity, the plurality of channels opening into the chamber; forming a lid from a third piece of silicon by forming a second cavity, wherein the second cavity extends upward from a bottom into the third piece of silicon; bonding the bottom of the third silicon die to the top of the first silicon die such that the second cavity surrounds the diaphragm.

In some embodiments, the depth of the second cavity is cut to mechanically limit the displacement of the diaphragm to less than 3 times the full range pressure displacement. In some methods, the depth of the second cavity is less than or equal to 0.9 μ ι η,1.1 μ ι η,1.3 μ ι η, or 1.5 μ ι η.

In other embodiments, a conductive layer may also be formed in the bottom of the cavity of the third silicon wafer. The conductive layer may be in electrical communication with a contact located on top of the third silicon die. Additionally, a conductive layer may also be formed on top of the membrane of the first silicon wafer. The conductive layer may be positioned such that when the diaphragm reaches a maximum displacement state, the conductive layer on top of the diaphragm is in electrical communication with the conductive layer on the bottom of the cavity within the third silicon and completes a circuit that may be used to detect this maximum displacement state.

In some embodiments of the method, the dielectric layer is formed of silicon dioxide or silicon nitride or a combination of silicon dioxide and silicon nitride. Also, in some embodiments of the method, the pressure sensor assembly is coupled to a base of the bottom of the support.

As will be described more fully below, these embodiments of the pressure sensors described herein ameliorate or mitigate some of the aforementioned problems. Further aspects, objects, desirable features, and advantages of the devices and methods disclosed herein will be better understood with reference to the following detailed description and accompanying drawings, which illustrate various embodiments by way of example only. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the claimed invention.

Drawings

FIG. 1 illustrates an isometric view of one embodiment of a pressure sensor assembly mounted on a substrate.

Fig. 2 shows a cross-sectional view of the pressure sensor assembly of fig. 1.

Fig. 3 shows a partial enlarged view of the cross-sectional view of fig. 2.

FIG. 4 illustrates a plurality of cross-sectional views of a silicon wafer in the process of forming one embodiment of a sensor.

FIG. 5 illustrates a plurality of cross-sectional views of a silicon wafer during the formation of one embodiment of a support.

Fig. 6 shows a cross-sectional view of the combination of the sensor of fig. 4 and the support of fig. 5.

Fig. 6A shows the cross-section of fig. 6 with a conductive layer 57 added on the top surface of the pressure sensor.

FIG. 7 illustrates a plurality of cross-sectional views of a silicon wafer during the formation of one embodiment of a lid.

FIG. 7A illustrates a plurality of cross-sectional views of a silicon wafer in the process of forming one embodiment of a cap configured to electronically detect a state of maximum displacement of the diaphragm.

FIG. 8 illustrates a cross-sectional view of one embodiment of the sensor of FIG. 4 in combination with the support of FIG. 5 and the cover of FIG. 7 to form a sensor assembly.

Fig. 9 shows the sensor assembly of fig. 8 with both sides of the cover 52 cut away.

FIG. 10 illustrates a cross-sectional view of one embodiment of a sensor assembly designed to electronically detect maximum displacement of a diaphragm.

FIG. 11 illustrates a cross-sectional view of one embodiment of a sensor assembly in which the dielectric layer is configured differently than in the embodiment of FIG. 10.

Detailed Description

The description uses "top" and "bottom" to help provide the reader with an orientation. These terms are not meant to limit the scope of the embodiments to a particular directional orientation relative to gravity, but are merely used to provide a relative orientation and/or direction with respect to other elements or portions of a particular embodiment. For example, if a "top" direction is established, then the "bottom" is the opposite side of the top of the embodiment, and vice versa. Thus, "upward" is the direction from "bottom" to "top," and "downward" is the direction from "top" to "bottom.

FIG. 1 illustrates an isometric view of one embodiment of a pressure sensor assembly mounted on a substrate. In the embodiment shown in FIG. 1, the entire assembly 100 includes the pressure sensor assembly 50 and the substrate 10. Pressure sensor assembly 50 may be coupled to substrate 10 using a variety of different methods. In a preferred embodiment, the pressure sensor assembly 50 is bonded to the substrate 10 using eutectic bonding techniques, frit bonding techniques, or adhesive bonding techniques. The substrate 10 shown in fig. 1 is exemplary, and other sizes or shapes of substrates 10 may be used.

Pressure sensor assembly 50 includes a cover 52, a sensor 54 and a support 56. In embodiments including a base 10, a support 56 is coupled to the top of the base 10. Sensor 54 is coupled to the top of support 56 and cover 52 is coupled to the top of sensor 54.

In a preferred embodiment, the cover 52, the sensor 54 and the support 56 are all made of silicon (Si). In a more preferred embodiment, the cover 52, sensor 54 and support 56 are all made of silicon. Thus, the sensor assembly may comprise three stacked silicon wafers. In other embodiments, other materials may be used. Fabricating the components of the sensor assembly 50 from silicon is advantageous because advanced fabrication techniques, such as those used in micro-electromechanical systems (MEMS), can be used to fabricate the components thereof. Generally, the sensor assembly 50 may be a MEMS device.

The silicon wafers used in the preferred embodiment may typically be between 300 μm and 400 μm thick. In a preferred embodiment, the silicon wafer is 350 μm thick. In other embodiments, the silicon wafer used for the cover 52, sensor 54 and support 56 may have other thicknesses. In different embodiments, different thicknesses may be used for each component. In a preferred embodiment, the wafer has a crystal orientation with a Miller index of 100. However, other crystal orientations may be used in other embodiments.

In a preferred embodiment, the cover 52, sensor 54 and support 56 are all made from silicon wafers and bonded together using silicon bonding techniques. However, other bonding techniques may be used, particularly if the material used is not a silicon wafer, and possibly other bonding techniques.

A cross-sectional view of an embodiment of a pressure sensor assembly 50 including the substrate 10 of fig. 1 is shown in fig. 2. The pressure sensor assembly 50 is coupled to the substrate 10 at the bottom of the support 56. In the embodiment shown in fig. 2, the substrate comprises a channel 12 extending from the top 11 of the substrate 10 to the bottom 13 of the substrate 10. In other embodiments, other types of channels may be used. The channels in the substrate 10 may have a uniform diameter, or may comprise more than two different diameters, or may be square or rectangular or polygonal. The channels in the substrate 10 may have different designs, but should all provide communication from the bottom of the substrate 10 up to the bottom of the support 56.

As can be seen in fig. 2, the support 56 includes a plurality of ports 60 and the sensor 56 includes a cavity 58. Support 56 is coupled to sensor 54 such that cavity 58 becomes chamber 58. A plurality of ports 60 extend through the support 56 in the thickness direction. In a preferred embodiment, the openings of the ports are arranged such that they are open in the chamber 58. A plurality of ports 60 provide a path for pressure from the bottom of the support 56 up into the cavity 58.

Fig. 3 shows a partial enlarged view of the cross section of fig. 2. As can be seen in fig. 3, a plurality of ports 60 extend through the support 56. The ports 60 may also be referred to as channels or channel arrays. The use of multiple smaller ports 60 has an advantage over the use of a single larger port because the array of smaller ports 60 suppresses pressure spikes of the incoming media to protect sensor 54. In particular, the plurality of ports 60 suppresses pressure spikes to the diaphragm 59 of the pressure sensor 54. In the preferred embodiment, the plurality of ports 60 are constructed to have a significantly reduced diameter compared to a typical single larger port. In a preferred embodiment, the port 60 is formed by drilling the support 56 using a Deep Reactive Ion Etching (DRIE) tool or by ultrasonic drilling or by mechanical drilling. The shape of the port 60 may be circular or square or rectangular or polygonal. Flow velocity V in each channel_fIs the pressure P outside the chamber 58_outWith the pressure P in the chamber 58_inPressure difference Δ p therebetween, fluid density ρ, ratio of diameter D of the channel to length L of the channel, and coefficient of friction f of the channel_DAs a function of (c). The relationship is described by the following formula

To this end, the diameter and length of the port 60 are selected so that the media flow into the chamber is reduced as compared to a single large port. In a preferred embodiment, the maximum pressure differential that the sensor will use for the fluid, and the D/L ratio are selected so that the flow is reduced to one-tenth of the flow when a single large port is used. In other embodiments, other reduction ratios may be designed for it.

In the embodiment shown in fig. 3, five ports extend upwardly from the bottom of the support 56 to the chamber 58. However, in other embodiments, other numbers of ports may be used. In a preferred embodiment, 2 to 10 ports may be used. In another preferred embodiment, 5 to 10 ports may be used. In yet another embodiment, 5 to 50 ports may be used. In still other more complex embodiments, 50 or more ports may be used. .

In embodiments where the port is limited by the thickness of the support 56, the length of the port 60 is defined by the thickness of the silicon wafer. Thus, only the diameter needs to be selected. In a preferred embodiment, the diameter of the port is one percent or less of the maximum diameter of the chamber 58. In still other embodiments, the diameter of the port is 1/25-1/15 of the largest diameter of the chamber 58. In still other embodiments, the diameter of the port is 1/15-1/10 of the largest diameter of the chamber 58. In still other embodiments, the diameter of the port is 1/10-1/5 of the largest diameter of the chamber 58.

The plurality of ports 60 may be arranged such that the channel opening 15 is located at the top of the substrate 10, such that the channel opening 15 encompasses the plurality of port openings 60 on the bottom of the support 56. In other embodiments, some or more portions of the port opening 60 may be located outside of the passage opening 15.

As can be seen in fig. 3, the sensor 54 comprises a cavity 58. The cavity extends upwardly from the bottom surface of the sensor 54 to form a cavity bottom such that a diaphragm is formed between the cavity bottom and the top of the sensor 54. In a preferred embodiment, the bottom of the cavity extends toward the top surface of sensor 54 by a distance that is at least 80% of the distance to the top surface. In a more preferred embodiment, the bottom of the cavity extends toward the top surface of the sensor 54 by a distance of 85% to 95% of the distance to the top surface. The depth of cavity 58 determines the thickness of diaphragm 59 and thus the full range of pressure sensor 54. The thickness of the sensor 54 is the distance between the bottom surface and the top surface, and the sensor 54 has a midplane located midway between the top surface and the bottom surface. In the preferred embodiment, the cavity 58 extends upwardly toward the top surface, through the medial plane to form the cavity bottom.

The minimum thickness of the diaphragm 59 (or the maximum depth of the cavity 58) is dictated by the output target and is limited by the manufacturing process. There is no maximum thickness of the diaphragm 59 (or minimum depth of the cavity 58). In a preferred embodiment, the membrane 59 is typically 10 microns thick to 95% of the thickness of the sensor wafer.

Sensor 54 includes circuitry disposed on the top side of sensor 54. The circuit is used to measure the deflection of the diaphragm and thus the pressure. The circuit may be formed by the conductive layer 51. The conductive layer may be made of any metal. The conductive layer 51 is used to form the circuitry embedded in the silicon of the sensor. In a preferred embodiment, conductive layer 51 is a different conductive layer than conductive layer 57 (shown in FIG. 6A). In some embodiments, they may be made of different materials and/or have different thicknesses. In other embodiments, conductive layer 57 may be formed as part of circuitry 51 or may be connected thereto.

To electrically isolate the circuit from potential shorting, a dielectric layer may be used between the sensor 54 and the support 56. In a preferred embodiment, a dielectric layer covers the bottom side of sensor 54 and cavity 58. The dielectric layer may be made of any insulating material. In a preferred embodiment, the dielectric layer is made of silicon dioxide or silicon nitride.

The primary source of electrical shorts is when a conductive fluid at a high potential enters the sensor assembly and impinges on the silicon surface creating a short circuit. Contact between the high potential fluid and the silicon may cause large currents to flow through the sensor, resulting in damage to the sensor and/or circuitry connected thereto. Thus, the electrical circuit needs to be electrically isolated from the cavity and channels in which the incoming fluid resides. This may be accomplished as shown in the cross-section of the sensor assembly 50 in fig. 11, where the dielectric layer 30 covers the entire bottom surface of the sensor. In a preferred embodiment, this includes the surface of the cavity 58 and the surface between the sensor 54 and the support 56. In another embodiment, the same electrical insulation may be achieved by applying a dielectric layer on all surfaces exposed to the inflowing fluid, as can be seen in the cross-sectional view of the sensor assembly 50 shown in FIG. 10. In a preferred embodiment, this may include the entire surface of chamber 58 and port 60.

Returning to fig. 3, a cover 52 is coupled to the top of the sensor 54. In the preferred embodiment, the cover 52 also includes a cavity 62. Cavity 62 is cut into cover 52 on the side coupled to sensor 54. The cavity 62 extends upwardly into the cover to form a cavity bottom. Thus, when the cover 52 is assembled to the sensor 54, the cavity 62 forms a gap above the diaphragm 59. In a preferred embodiment, the cavity 62 in the lid 52 is sized and positioned such that the cavity 62 surrounds the bottom of the diaphragm 59. Also in the preferred embodiment, the depth of the cavity 62 is designed such that the bottom of the cavity 62 limits the movement of the diaphragm 59 toward the cover 52. Thus, the cavity is sized and positioned such that when the cover is coupled to the sensor 54, the bottom of the cavity 62 acts as a mechanical stop to prevent excessive displacement of the diaphragm 59.

In the preferred embodiment, diaphragm 59 typically moves about 0.3-0.5 μm at full range pressure. For effective stopping, the gap formed by cavity 62 needs to be greater than the full range of displacement, but less than the distance where the diaphragm would yield or burst if no stop were present. Diaphragm yielding or rupture typically occurs over a 3 to 5 times full scale pressure displacement. Thus, for a typical full scale pressure displacement of 0.3 μm, the depth of the cavity 62 may be greater than 0.3 μm but less than 0.9 μm. In yet another embodiment, where the typical full scale pressure displacement of the diaphragm is 0.3 μm, the depth of the cavity 62 may be greater than 0.3 μm but less than 1.5 μm. In other embodiments, other cavity depths may be used depending on the design of the diaphragm.

A set of drawings will now be described to illustrate a process of constructing one embodiment of a pressure sensor assembly 50. In this embodiment, the pressure sensor assembly 50 would be constructed of 3 separate silicon wafers bonded together. Pressure sensor assembly 50 will include a plurality of ports 60, a cover 52 with mechanical stops, and a dielectric layer that electrically insulates sensor 54 from support 56. In other embodiments, other combinations or configurations may be constructed.

FIG. 4 illustrates a plurality of cross-sectional views of a silicon wafer in the process of forming one embodiment of sensor 54. In step 1, the process preferably starts with an n-type <100> Si wafer with a resistance of 10 Ω cm +/-20% and a thickness of 350 μm. In step 2, an oxide layer is added with the SiN deposition. In a preferred embodiment, photoresist spin coating is performed. The cavity mask is formed by a properly placed and sized SiN etch and oxide etch, followed by a photoresist strip. In step 3, a KOH etch is used to create cavity 58 of sensor 54 and, thus, diaphragm 59. The KOH etch preferably etches to a depth of 90% of the wafer thickness. Rounding is also preferably performed in this step (corner rounding). In step 4, the SiN and oxide layers are stripped.

FIG. 5 illustrates a plurality of cross-sectional views of a silicon wafer during the formation of one embodiment of the support 56. In step 1, the method preferably starts with a <100> Si wafer having a thickness of 350 μm. In step 2, a mask of a plurality of ports 60 is formed by: an oxide layer is applied, a photoresist spin coating is performed, then the port mask is exposed, and an oxide etch is performed. In step 3, a plurality of ports 60 are formed by first performing a Deep Reactive Ion Etch (DRIE) followed by a photoresist strip. Finally, in step 4, the oxide layer is stripped.

Fig. 6 shows a cross-sectional view of the sensor 54 of fig. 4 in combination with the support 56 of fig. 5. In the preferred embodiment, two silicon wafers are silicon-to-silicon bonded and the assembly is then oxidized in preparation for forming a circuit for detecting diaphragm displacement on the top surface of sensor 54. A series of steps are performed to form the circuit, as is well known to those skilled in the art. This series of steps includes depositing a metal and patterning the metal, for example, aluminum. This patterned metal may not only form a circuit, it may also serve as part of the electrical contacts that form the maximum displacement detection switch (maximum displacement detection switch) on the top side of the diaphragm 59.

Fig. 6A shows the cross-section of fig. 6, where conductive layer 57 is applied on the top surface of pressure sensor 54. As can be seen in fig. 6A, a portion of the conductive layer may be formed over the diaphragm 59 to provide electrical contact for the maximum displacement detection switch.

FIG. 7 illustrates a plurality of cross-sectional views of a silicon wafer forming one embodiment of the lid 52. In step 1, the method preferably starts with a <100> Si wafer having a resistance of 0.1. omega. cm or less and a thickness of 350 μm. In step 2, photoresist spin coating is performed first, followed by the formation of a recess mask. The cavity 62 is formed by DRIE. Then, photoresist stripping is performed.

FIG. 7A illustrates multiple cross-sections of a silicon wafer in the process of forming one embodiment of a cap configured to electronically detect a maximum displacement state of the diaphragm. In a preferred embodiment, the cover 52 may not only act as a mechanical stop, but may also be configured to act as an electrical detection switch. In such an embodiment, the cavity 62 is covered with a conductive layer 63, the conductive layer 63 being electrically connected to the cover 52. The conductive layer may be made of any metal. Thus, when the membrane 59 reaches the bottom of the cavity 62, the conductive layer 57 on the membrane 59 will be in contact with the conductive layer 63 in the cavity of the cover 52. Preferably, the contact forms a closed circuit that can be detected by a detection circuit that can disable the high pressure source or relieve the pressure by opening another valve.

As can be seen in fig. 7A, in step 3, a conductive layer, for example aluminum, is deposited on the underside of the lid 52. Spin coating of photoresist is then performed, followed by masking and etching steps. In step 4, a conductive layer, such as aluminum, is deposited on the top side of the lid 52, which can be used as an electrical contact to the conductive layer 63 on the top side of the lid 52, and then a photoresist spin coating is performed followed by masking and etching steps.

Fig. 8 shows a cross-section of sensor 54 in combination with support 56 and cover 52 to form sensor assembly 50. In a preferred embodiment, the cap 52 is silicon-to-silicon bonded to the top of the sensor 54. The stack of three silicon wafers bonded together may then be subjected to a titanium/platinum/gold deposition on the bottom side of the wafer stack. Fig. 9 shows the sensor assembly of fig. 8 with both sides of the cover 52 cut away.

FIG. 10 illustrates a cross-sectional view of one embodiment of a sensor assembly designed to electronically detect maximum displacement of a diaphragm. As can be seen in fig. 10, a conductive layer 63 is deposited on the bottom of the cavity 62 in the lid 52. In addition, a conductive layer 57 is deposited on top of the membrane 59. When the diaphragm is flexed to its maximum displacement, the two

conductive layers

57 and 63 contact and complete an electrical circuit. The completion of the circuit is detected and the system knows that the diaphragm has reached its maximum displacement. In a preferred embodiment, the detection of maximum displacement may cause an action to relieve or remove the overpressure condition.

As can also be seen in fig. 10, the dielectric layer covers the interior of the cavity 58 and the interior of the port/channel 60. Thus, the dielectric layer 30 electrically insulates the cavity 58 and the port/channel 60 from the sensor 54. As can be seen in this embodiment, the sensor 54 and the support 56 are directly coupled together.

FIG. 11 illustrates a cross-sectional view of one embodiment of a sensor assembly in which the dielectric layer is configured differently than the embodiment of FIG. 10. As can be seen in fig. 11, not all of the cavities 58 and ports 60 are covered, but rather the dielectric layer 30 covers the entire bottom surface of the sensor 54. Although the dielectric layer in the embodiment of fig. 11 has a different configuration, it has the same function of electrically insulating the sensor 54 from the support 56. As can be seen in fig. 11, in such an embodiment, the sensor 54 is not directly coupled to the support 56 because the dielectric layer 30 is placed between them.

Although embodiments of the present invention have been described with reference to preferred configurations and specific examples, those skilled in the art will readily appreciate that many modifications and adaptations to the pressure sensor and its method of manufacture may be made without departing from the spirit and scope of the embodiments as hereinafter claimed. Accordingly, it should be clearly understood that the present description is made only by way of example and not as a limitation on the scope of the embodiments as claimed below.

Claims

1. A pressure sensor assembly comprising:

a first silicon wafer having a top and a bottom;

a cavity formed within the first silicon die, the cavity extending upward from a bottom of the first silicon die toward a top of the first silicon die forming a cavity bottom such that a diaphragm is formed between the cavity bottom and the top of the first silicon die;

a circuit formed of a conductive layer disposed on the top of the first silicon wafer;

a second silicon die coupled along the bottom of the first silicon die and covering the cavity to form a chamber;

a dielectric layer electrically insulating the interior of the chamber from the first silicon wafer;

a plurality of ports located within a region of the top of the second die defined by the cavity, the plurality of ports extending through the second die to the bottom of the second die;

a third piece of silicon coupled to the top of the first piece of silicon such that the third piece of silicon covers the diaphragm; and

a second cavity cut into the bottom of the third silicon die, wherein the second cavity is sized and positioned such that the second cavity surrounds the diaphragm.

2. The pressure sensor assembly of claim 1, wherein the depth of the second cavity is designed to mechanically limit displacement of the diaphragm to less than 3 times a full scale pressure displacement.

3. The pressure sensor assembly of claim 1, further comprising an electrical contact located at a top of the diaphragm and a second electrical contact located at a bottom of the second cavity.

4. The pressure sensor assembly of claim 3, wherein the electrical contact will contact the second electrical contact and form a closed circuit when the diaphragm moves to full depth within the second cavity.

5. The pressure sensor assembly of claim 1, wherein the depth of the second cavity is less than or equal to 0.9 μ ι η.

6. The pressure sensor assembly of claim 1, wherein the bottom of the cavity is located at least 80% of the distance to the top of the first silicon die.

7. The pressure sensor assembly of claim 1, wherein the dielectric layer is made of silicon dioxide or silicon nitride.

8. The pressure sensor assembly of claim 1, further comprising a base coupled to the bottom of the second silicon die, the base including a channel extending from the top of the base to the bottom of the base, and wherein an opening of the channel at the top of the base encompasses openings of the plurality of ports at the bottom of the second silicon die.

9. The pressure sensor assembly of claim 1, wherein the dielectric layer separates the first silicon piece from the second silicon piece.

10. The pressure sensor assembly of claim 1, wherein the dielectric layer covers an interior of the chamber.

11. A pressure sensor assembly comprising:

a first silicon wafer having a top surface and a bottom surface and an intermediate plane defined at an intermediate location between the top surface and the bottom surface, wherein the bottom surface includes a cavity extending upwardly toward the top surface, through the intermediate plane forming a cavity bottom;

a diaphragm formed between the cavity bottom and the top surface;

a second silicon die coupled to the bottom surface of the first silicon die, the second silicon die covering the cavity to form a chamber;

a plurality of channels extending through the second silicon wafer and into the chamber;

a third silicon die coupled to the top surface of the first silicon die, the third silicon die comprising a second cavity sized and positioned to cover the diaphragm, and wherein a bottom of the second cavity forms a mechanical stop for the diaphragm;

and wherein the chamber is electrically insulated from the first silicon wafer by a dielectric layer.

12. The pressure sensor assembly of claim 11, wherein the depth of the second cavity is less than or equal to 0.9 μ ι η.

13. The pressure sensor assembly of claim 11, wherein the cavity bottom extends toward the top surface of the first die by a distance that is at least 80% of the distance to the top surface.

14. The pressure sensor assembly of claim 11, wherein the dielectric layer is made of silicon dioxide or silicon nitride.

15. The pressure sensor assembly of claim 11, further comprising an electrical contact located at a top of the diaphragm and a second electrical contact located at a bottom of the second cavity.

16. The pressure sensor assembly of claim 11, further comprising a substrate coupled to a bottom side of the second silicon die, the substrate including a substrate channel extending from a top of the substrate to a bottom of the substrate, and wherein a substrate channel that is open at the top of the substrate covers channel openings of a plurality of the channels located within the second silicon die.

17. A sensor assembly, comprising:

a sensor having a diaphragm, the sensor having a top and a bottom;

a cover coupled to the top of the sensor and forming a gap on the diaphragm, the gap designed to limit full range movement of the diaphragm;

a support coupled to a bottom of the sensor, wherein the support and the sensor form a chamber adjacent to the diaphragm, and wherein the support comprises a plurality of channels that pass from the bottom of the support up through the support into the chamber; and the combination of (a) and (b),

a dielectric layer electrically insulating the chamber and the plurality of channels from the sensor.

18. The pressure sensor assembly of claim 17, wherein the gap is less than or equal to 0.9 μ ι η.

19. The pressure sensor assembly of claim 17, further comprising an electrical contact located on a top of the diaphragm and a second electrical contact located on a bottom of the cover over the gap.

20. The pressure sensor assembly of claim 17, wherein said dielectric layer separates said sensor from said support.

21. A method of manufacturing a pressure sensor assembly, comprising:

forming a sensor from a first silicon wafer by forming a cavity extending from a bottom up into the first silicon wafer, a diaphragm being formed between the bottom of the cavity and a top of the sensor;

forming a conductive layer on the top of the first silicon wafer;

forming a support from a second silicon wafer by forming a plurality of channels, wherein the plurality of channels pass through the second silicon wafer from a top surface to a bottom surface;

bonding the bottom of the first silicon wafer to the top surface of the second silicon wafer such that a chamber is formed by the cavity, the plurality of channels opening into the chamber;

forming a dielectric layer that electrically insulates the chamber from the sensor;

forming a lid from a third piece of silicon by forming a second cavity, wherein the second cavity extends upward from a bottom into the third piece of silicon; and

bonding the bottom of the third silicon die to the top of the first silicon die such that the second cavity surrounds the diaphragm.

22. The method of manufacturing a pressure sensor assembly of claim 21, wherein the depth of the second cavity is cut to mechanically limit the displacement of the diaphragm to less than 3 times a full scale pressure displacement.

23. The method of making a pressure sensor assembly of claim 21, wherein the depth of the second cavity is less than or equal to 0.9 μ ι η.

24. The method of manufacturing a pressure sensor assembly of claim 21, wherein the dielectric layer is made of silicon dioxide or silicon nitride.

25. The method of manufacturing a pressure sensor assembly of claim 21, wherein the dielectric layer separates the sensor from the support.

26. The method of manufacturing a pressure sensor assembly of claim 21, wherein the dielectric layer covers a surface of the chamber.

27. The method of manufacturing a pressure sensor assembly of claim 21, further comprising bonding a substrate to the bottom surface of the support, wherein the substrate includes a channel extending from a top of the substrate to a bottom of the substrate, and wherein a channel opening at the top of the substrate encompasses the plurality of channels of the bottom surface of the support.

28. The method of making a pressure sensor assembly of claim 21, further comprising forming a conductive layer on a bottom of the second cavity of the third silicon die.

29. The method of manufacturing a pressure sensor assembly of claim 21, further comprising forming electrical contacts on a top of the third silicon die, the electrical contacts being connected to the conductive layer on a bottom of the second cavity of the third silicon die.

30. The method of manufacturing a pressure sensor assembly of claim 21, wherein when the diaphragm is moved to the full depth of the second cavity, the conductive layer of the top side of the diaphragm contacts the conductive layer of the bottom of the second cavity and forms a closed circuit.

31. A method of manufacturing a pressure sensor assembly, comprising:

forming a sensor from a first silicon wafer, wherein the sensor comprises a diaphragm;

forming a conductive layer on top of the sensor, forming a circuit on top of the sensor;

forming a support from a second silicon wafer;

bonding a bottom of the first silicon die to a top surface of the second silicon die such that a chamber is formed enclosed by the first silicon die and the second silicon die;

forming a plurality of channels through the second wafer from the chamber to a bottom surface of the second wafer;

forming a cap from a third silicon wafer; and

bonding the bottom of the third silicon die to the top of the first silicon die such that a gap on the diaphragm is between the sensor and the cover.

32. The method of manufacturing a pressure sensor assembly of claim 31, wherein the gap is less than 3 times a full range pressure displacement of the diaphragm.

33. The method of making a pressure sensor assembly of claim 31, wherein the gap is less than or equal to 0.9 μ ι η.

34. The method of manufacturing a pressure sensor assembly of claim 31, wherein the dielectric layer is made of silicon dioxide or silicon nitride.

35. The method of manufacturing a pressure sensor assembly of claim 31, wherein the dielectric layer separates the sensor from the support.

36. The method of manufacturing a pressure sensor assembly of claim 31, wherein the dielectric layer covers a surface of the chamber.

37. The method of manufacturing a pressure sensor assembly of claim 31, further comprising forming a second conductive layer on a surface of the gap on the diaphragm opposite the conductive layer.

38. The method of making a pressure sensor assembly of claim 37, further comprising forming electrical contacts on an upper portion of the third silicon die in electrical communication with the second conductive layer.

39. The method of manufacturing a pressure sensor assembly of claim 37, wherein when the diaphragm moves to the full depth of the chamber, the conductive layer contacts the second conductive layer and forms a closed circuit.