Micro thermal conductivity detector with on-chip Wheatstone bridge and preparation method thereof

Abstract

The present invention provides a micro thermal conductivity detector with an on-chip Wheatstone bridge and a preparation method thereof. A conductive connector is integrated in a substrate to replace an external lead, thereby reducing the contact resistance generated by the external lead, reducing noise interference of the detector, and improving the signal-to-noise ratio of the detector, thereby reducing the detection limit of the detector. In addition, only four pad interfaces are provided externally, which is convenient for the use of the device.

Description

Technical Field

[0001] The invention belongs to the field of micro-electromechanical systems, and relates to a micro-thermal conductivity detector with an on-chip Wheatstone bridge and a preparation method thereof. Background Art

[0002] The thermal conductivity detector realizes detection based on the difference in thermal conductivity of different gases. The micro thermal conductivity detector has the advantages of high sensitivity, small size and low power consumption, and can meet the needs of miniaturization of gas chromatography systems.

[0003] The micro thermal conductivity detector is composed of a micro channel and a thermistor. The commonly used micro thermal conductivity detector includes two micro channels, namely the reference micro channel and the measurement micro channel. Four identical thermistors are connected to form a Wheatstone bridge to increase the sensitivity and anti-interference ability of the device. Among them, one set of thermistors in the Wheatstone bridge is placed in the reference micro channel, and the other set of thermistors is placed in the measurement micro channel. When the two micro channels continue to pass through the same carrier gas, the Wheatstone bridge is balanced and there is no output signal. When the carrier gas carries the sample gas to be tested through the measurement micro channel, the thermal conductivity of the gas changes, causing the thermistor to change, and the Wheatstone bridge is unbalanced and outputs an electrical signal, thereby obtaining a gas chromatogram.

[0004] Existing micro-thermal conductivity detectors are usually composed of four thermistors, and the external electrical interface is eight metal pads, which are connected to form a Wheatstone bridge by bonding wires on the pads. This off-chip connection method introduces contact resistance. On the one hand, the inconsistency of contact resistance will increase the zero-point error of the Wheatstone bridge. On the other hand, the interference signal introduced by the contact resistance will reduce the signal-to-noise ratio of the device and limit the further reduction of the device detection limit. In addition, the external leads need to be connected to form a Wheatstone bridge in a specific way, which is inconvenient to use.

[0005] Therefore, it is necessary to provide a micro thermal conductivity detector with an on-chip Wheatstone bridge and a preparation method thereof. Summary of the invention

[0006] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a micro-thermal conductivity detector with an on-chip Wheatstone bridge and a preparation method thereof, so as to solve the problems of low signal-to-noise ratio and inconvenience in use of the micro-thermal conductivity detector in the prior art due to its structure.

[0007] To achieve the above objectives and other related objectives, the present invention provides a micro thermal conductivity detector with an on-chip Wheatstone bridge, the micro thermal conductivity detector comprising:

[0008] A substrate, wherein a reference microchannel and a measurement microchannel are disposed in the substrate;

[0009] Thermistors, the thermistors comprising a first thermistor and a fourth thermistor suspended in the measuring microchannel through a supporting structure and arranged along the airflow direction, and a second thermistor and a third thermistor suspended in the reference microchannel through the supporting structure and arranged along the airflow direction;

[0010] A conductive connector, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, wherein the conductive connector includes a first lead, a second lead, and a stacked crossover structure that are insulated and located on the substrate between the reference microchannel and the measurement microchannel, wherein the first lead connects the first thermistor and the second thermistor, and the second lead connects the third thermistor and the fourth thermistor, and the stacked crossover structure includes a first insulating layer, a bottom lead, a second insulating layer, and a top crossover from bottom to top, wherein the bottom lead connects the first thermistor and the third thermistor, and the top crossover penetrates the second insulating layer to connect the second thermistor and the fourth thermistor;

[0011] A cover plate is bonded to the substrate, and the reference microchannel and the measuring microchannel are covered by the cover plate to form a reference closed microchannel and a measuring closed microchannel.

[0012] Optionally, the support structure is in a mesh shape; the support structure includes a first dielectric layer located on the lower surface of the thermistor and a second dielectric layer located on the upper surface of the thermistor.

[0013] Optionally, the pad in the conductive connecting member is exposed on the cover plate; the conductive connecting member and the thermistor are made of the same material.

[0014] Optionally, the cover plate is arranged on two opposite sides of the substrate, or the cover plate is only arranged on one side of the substrate; a cover plate receiving groove is arranged on one side of the cover plate adjacent to the substrate.

[0015] Optionally, the substrate includes a silicon substrate, a silicon-on-insulator substrate, a ceramic substrate or a glass substrate; and the cover plate includes a silicon cover plate, a silicon-on-insulator cover plate, a ceramic cover plate or a glass cover plate.

[0016] The present invention also provides a method for preparing a micro thermal conductivity detector having an on-chip Wheatstone bridge, comprising the following steps:

[0017] providing a substrate;

[0018] Thermistors, conductive connectors and supporting structures are formed on the substrate, wherein the thermistors include a first thermistor, a second thermistor, a third thermistor and a fourth thermistor, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, the conductive connector includes an insulated first lead, a second lead and a stacked crossover structure, the first lead connects the first thermistor and the second thermistor, the second lead connects the third thermistor and the fourth thermistor, the stacked crossover structure includes a stacked first insulating layer, a bottom lead, a second insulating layer and a top crossover from bottom to top, the bottom lead connects the first thermistor and the third thermistor, the top crossover penetrates the second insulating layer and connects the second thermistor and the fourth thermistor;

[0019] Providing an upper cover plate, and bonding the upper cover plate to the upper surface of the substrate;

[0020] The substrate is patterned from the lower surface of the substrate to form a reference microchannel and a measuring microchannel, the first lead, the second lead and the stacked cross-wire structure are located on the substrate between the reference microchannel and the measuring microchannel, and the first thermistor and the fourth thermistor are suspended in the measuring microchannel through the support structure and arranged along the airflow direction, and the second thermistor and the third thermistor are suspended in the reference microchannel through the support structure and arranged along the airflow direction;

[0021] A lower cover plate is provided and bonded to the lower surface of the substrate, and the upper cover plate and the lower cover plate are combined to cover the reference microchannel and the measurement microchannel to form a reference closed microchannel and a measurement closed microchannel.

[0022] The present invention also provides a method for preparing a micro thermal conductivity detector having an on-chip Wheatstone bridge, comprising the following steps:

[0023] providing a substrate;

[0024] Thermistors, conductive connectors and supporting structures are formed on the substrate, wherein the thermistors include a first thermistor, a second thermistor, a third thermistor and a fourth thermistor, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, and the conductive connector includes a first lead, a second lead and a stacked crossover structure on the substrate that are insulated, wherein the first lead connects the first thermistor and the second thermistor, the second lead connects the third thermistor and the fourth thermistor, and the stacked crossover structure includes a first insulating layer, a bottom lead, a second insulating layer and a top crossover stacked from bottom to top, wherein the bottom lead connects the first thermistor and the third thermistor, and the top crossover penetrates the second insulating layer to connect the second thermistor and the fourth thermistor;

[0025] The substrate is patterned to form a reference microchannel and a measuring microchannel with the bottom located in the substrate, the first lead, the second lead and the stacked cross-wire structure are located on the substrate between the reference microchannel and the measuring microchannel, and the first thermistor and the fourth thermistor are suspended in the measuring microchannel through the support structure and arranged along the airflow direction, and the second thermistor and the third thermistor are suspended in the reference microchannel through the support structure and arranged along the airflow direction;

[0026] An upper cover plate is provided and bonded to the upper surface of the substrate, and the reference microchannel and the measurement microchannel are covered by the upper cover plate to form a reference closed microchannel and a measurement closed microchannel.

[0027] Optionally, during bonding, the substrate has a substrate accommodating groove, and / or the upper cover plate has a cover plate accommodating groove.

[0028] Optionally, the support structure is formed in a mesh structure.

[0029] Optionally, the first lead, the second lead, the bottom lead and the pad are prepared while preparing the thermistor; the pad is exposed on the upper cover.

[0030] As described above, the micro-thermal conductivity detector with an on-chip Wheatstone bridge and the preparation method thereof of the present invention integrates a conductive connector in the substrate to replace the external leads, thereby reducing the contact resistance generated by the external leads, reducing the zero point error and noise interference of the detector, and improving the signal-to-noise ratio of the detector, thereby reducing the detection limit of the detector, and only provides four pad interfaces to the outside, which is convenient for the use of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1It shows a schematic diagram of the three-dimensional structure of a micro thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon substrate in the first and second embodiments of the present invention.

[0032] Figure 2 Display as Figure 1 Schematic diagram of the thermistor and supporting structure.

[0033] Figure 3a , Figure 3b and Figure 4 Display as Figure 1 Schematic diagram of the Wheatstone bridge layout.

[0034] Figure 5 It shows a process flow chart of preparing a micro thermal conductivity detector with an on-chip Wheatstone bridge in Example 1 of the present invention.

[0035] Figure 6 to Figure 10 It shows a schematic structural diagram of the steps of preparing a micro-thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon substrate in the first embodiment of the present invention.

[0036] Fig.11 It shows a process flow chart of preparing a micro thermal conductivity detector with an on-chip Wheatstone bridge in the second embodiment of the present invention.

[0037] Figure 12-13 It shows a schematic structural diagram of the steps of preparing a micro-thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon substrate in the second embodiment of the present invention.

[0038] Figure 14 to Figure 18 It shows a schematic structural diagram of the steps of preparing a micro-thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon-on-insulator substrate in the third embodiment of the present invention.

[0039] Figure 19 to Figure 21 It shows a schematic structural diagram of the steps of preparing a micro-thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon-on-insulator substrate in the fourth embodiment of the present invention.

[0040] Description of Reference Numerals

[0041] 100 Silicon substrate

[0042] 110 Silicon oxide layer

[0043] 120 substrate receiving groove

[0044] 210 Glass cover

[0045] 211 Cover plate receiving groove

[0046] 220 Glass lower cover

[0047] 301 Reference Microchannel

[0048] 302 Measuring Microchannels

[0049] 311 Reference Closed Microchannel

[0050] 312 Measuring closed microchannels

[0051] 400 Thermistor

[0052] 401 First thermistor

[0053] 402 Second thermistor

[0054] 403 The third thermistor

[0055] 404 Fourth thermistor

[0056] 501 First Lead

[0057] 502 Second lead

[0058] 503 stacking spanning structure

[0059] 513 Bottom lead

[0060] 523 Second insulation layer

[0061] 533 Top Crossover

[0062] 543 First insulation layer

[0063] 504 pad

[0064] 601 First dielectric layer

[0065] 602 Second dielectric layer

[0066] 111 Silicon-on-insulator substrate

[0067] 101 Bottom Silicon

[0068] 102 buried oxygen layer

[0069] 103 Top Silicon

[0070] 700 protective layer DETAILED DESCRIPTION

[0071] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0072] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0073] For ease of description, spatial relational terms such as “under”, “below”, “below”, “below”, “over”, etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatial relational terms are intended to include other orientations of the device in use or operation in addition to the orientation depicted in the drawings, and may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, so that the first and second features may not be in direct contact. In addition, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or one or more intervening layers may also be present.

[0074] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0075] Embodiment 1

[0076] See also Figures 1 to 10The present embodiment provides a micro thermal conductivity detector with an on-chip Wheatstone bridge, the micro thermal conductivity detector comprising: a substrate, a thermistor 400, a conductive connector and a cover plate, the substrate being provided with a reference microchannel 301 and a measuring microchannel 302; the thermistor 400 comprising a first thermistor 401 and a fourth thermistor 404 suspended in the measuring microchannel 302 by a supporting structure and arranged along the airflow direction, and a second thermistor 402 and a third thermistor 403 suspended in the reference microchannel 301 by the supporting structure and arranged along the airflow direction; the conductive connector connects the thermistors 400 to form a Wheatstone bridge, the conductive connector comprising a first lead 501 and a second lead 502 on the substrate being insulated and located between the reference microchannel 301 and the measuring microchannel 302. and a stacked crossover structure 503, wherein the first lead 501 connects the first thermistor 401 and the second thermistor 402, and the second lead 502 connects the third thermistor 403 and the fourth thermistor 404. The stacked crossover structure 503 includes, from bottom to top, a stacked first insulating layer 543, a bottom lead 513, a second insulating layer 523 and a top crossover 533, and the bottom lead 513 connects the first thermistor 401 and the third thermistor 403, and the top crossover 533 penetrates the second insulating layer 523 to connect the second thermistor 402 and the fourth thermistor 404; the cover plate is bonded to the substrate, and the reference microchannel 301 and the measurement microchannel 302 are covered by the cover plate to form a reference closed microchannel 311 and a measurement closed microchannel 312.

[0077] Specifically, in this embodiment, the first thermistor 401 is represented by R1, the second thermistor 402 is represented by R2, the third thermistor 403 is represented by R3, and the fourth thermistor 404 is represented by R4. The first thermistor 401 and the fourth thermistor 404 are suspended in the measuring microchannel 302 through the supporting structure and are arranged along the airflow direction, preferably suspended in the center of the measuring microchannel 302 and placed parallel to the airflow direction; the second thermistor 402 and the third thermistor 403 are suspended in the reference microchannel 301 through the supporting structure and are arranged along the airflow direction, preferably suspended in the center of the reference microchannel 301 and placed parallel to the airflow direction.

[0078] The conductive connection is located on the substrate, including the first lead 501, the second lead 502 and the stacked jumper structure 503 on the substrate, which are insulated and located between the reference microchannel 301 and the measuring microchannel 302. The stacked jumper structure 503 includes the stacked first insulating layer 543, the bottom lead 513, the second insulating layer 523 and the top jumper 533 from bottom to top. The first lead 501 connects the first thermistor 401 and the second thermistor 402, the second lead 502 connects the third thermistor 403 and the fourth thermistor 404, the bottom lead 513 connects the first thermistor 401 and the third thermistor 403, and the top crossover 433 penetrates the second insulating layer 523 to connect the second thermistor 402 and the fourth thermistor 404, so that the thermistors 400 are connected through the conductive connector to form the Wheatstone bridge, and the pads 504 connected to the Wheatstone bridge are recorded as Pad1, Pad2, Pad3, and Pad4, wherein Pad1 and Pad3 serve as power terminals, and Pad2 and Pad4 serve as signal terminals.

[0079] In this embodiment, since the conductive connector is integrated into the substrate, it can replace the external lead for electrical connection, thereby reducing the contact resistance generated by the external lead, reducing the zero point error and noise interference of the detector, and lowering the detection limit of the detector.

[0080] Furthermore, the pads 504 in the conductive connector are preferably exposed on the cover plate, so that the interfaces of the four pads 504 can facilitate electrical connection and use of the device, but the position setting of the pads 504 is not limited to this.

[0081] As an example, the substrate may include a silicon substrate 100 , a silicon-on-insulator substrate, a ceramic substrate or a glass substrate; the cover plate may include a silicon cover plate, a silicon-on-insulator cover plate, a ceramic cover plate or a glass cover plate.

[0082] For details, see Figures 1 to 10 In this embodiment, the substrate adopts the silicon substrate 100, and the cover plate adopts a glass cover plate, and the cover plates are arranged on opposite sides of the substrate, that is, they include a glass upper cover plate 210 and a glass lower cover plate 220, but the material selection of the micro thermal conductivity detector is not limited thereto. As needed, the silicon substrate 100 can also be replaced with a silicon-on-insulator substrate, a ceramic substrate, or a glass substrate, etc., the glass upper cover plate 210 can also be replaced with a silicon upper cover plate, a silicon upper cover plate on an insulator, or a ceramic upper cover plate, etc., and the glass lower cover plate 220 can also be replaced with a silicon lower cover plate, a silicon lower cover plate on an insulator, or a ceramic lower cover plate, etc.

[0083] As an example, a cover plate receiving groove 211 is provided on one side of the cover plate adjacent to the base plate.

[0084] For details, see Fig.10 As required, the glass upper cover plate 210 is provided with the cover plate receiving groove 211 on the side adjacent to the silicon substrate 100 to provide sufficient space for the support structure and the conductive connecting member, but it is not limited thereto. When the silicon substrate 100 can provide sufficient space, the cover plate receiving groove 211 may not be provided in the glass upper cover plate 210. No excessive limitation is made here.

[0085] As an example, the support structure is a mesh structure.

[0086] For details, see Figure 2 , Figure 3a and Figure 3b The support structure is suspended in the reference microchannel 301 and the measurement microchannel 302, and preferably the support structure is suspended in the center of the microchannel and placed parallel to the airflow direction. When the support structure adopts a mesh structure, the contact area of ​​the thermistor 400 located on the support structure can be increased to increase the sensitivity. Of course, the support structure can also adopt other morphologies as needed, and no excessive restrictions are made here.

[0087] As an example, the support structure includes a first dielectric layer 601 and a second dielectric layer 602 stacked from bottom to top.

[0088] In this embodiment, the support structure is composed of the first dielectric layer 601 and the second dielectric layer 602. The first dielectric layer 601 serves as a support layer, and the second dielectric layer 602 serves as a protective layer. The first dielectric layer 601 may include one or a combination of a silicon oxide layer and a silicon nitride layer, and the second dielectric layer 602 may include one or a combination of a silicon oxide layer and a silicon nitride layer, which may be selected according to needs.

[0089] As an example, the conductive connecting member 500 and the thermistor 400 are made of the same material, or different materials may be used.

[0090] In which, the conductive connector is formed on the upper surface of the silicon substrate 100, and the first lead 501, the second lead 502, the stacked jumper structure 503 and the pad 504 are all insulated from the silicon substrate 100 by the first dielectric layer 601, and in the stacked jumper structure 503, the bottom lead 513 and the top jumper 533 are insulated by the second insulating layer 523. In this embodiment, in order to reduce the process complexity, the first insulating layer 543 is the patterned first dielectric layer 601, and the second insulating layer 523 is the patterned second dielectric layer 602, but it is not limited to this.

[0091] The material used for the thermistor 400 may include one of a Pt / Ti stack, a Ni / Cr stack, a W / Ti stack, and a W / Re stack, which may be selected as needed. The material used for the conductive connector may include one of a Pt / Ti stack, a Ni / Cr stack, a W / Ti stack, a W / Re stack, an Al / Ti stack, and an Au / Ti stack. It is preferred that the conductive connector and the thermistor 400 are made of the same material to simplify the process, which may be selected as needed.

[0092] See also Figures 5 to 10 This embodiment also provides a method for preparing a micro thermal conductivity detector having an on-chip Wheatstone bridge, comprising the following steps:

[0093] S1: Provide substrate;

[0094] S2: forming a thermistor 400, a conductive connector and a supporting structure on the substrate, wherein the thermistor 400 includes a first thermistor 401, a second thermistor 402, a third thermistor 403 and a fourth thermistor 404, wherein the conductive connector connects the thermistors 400 to form a Wheatstone bridge, and the conductive connector includes an insulated first lead 501, a second lead 502 and a stacked crossover structure 503, wherein the first lead 501 connects the first thermistor 401 and the second thermistor 404. The second lead 502 connects the third thermistor 503 and the fourth thermistor 504, the stacked crossover structure 503 includes a first insulating layer 543, a bottom lead 513, a second insulating layer 523 and a top crossover 533 stacked from bottom to top, and the bottom lead 513 connects the first thermistor 401 and the third thermistor 403, and the top crossover 533 penetrates the second insulating layer 523 to connect the second thermistor 402 and the fourth thermistor 404;

[0095] S3: providing an upper cover plate, and bonding the upper cover plate to the upper surface of the substrate;

[0096] S4: Patterning the substrate from the lower surface of the substrate to form a reference microchannel 301 and a measuring microchannel 302, the first lead 501, the second lead 502 and the stacked cross-wire structure 503 are located on the substrate between the reference microchannel 301 and the measuring microchannel 302, and the first thermistor 401 and the fourth thermistor 404 are suspended in the measuring microchannel 302 through the supporting structure and are arranged along the airflow direction, and the second thermistor 402 and the third thermistor 403 are suspended in the reference microchannel 301 through the supporting structure and are arranged along the airflow direction;

[0097] S5: providing a lower cover plate, and bonding the lower cover plate to the lower surface of the substrate, combining the upper cover plate and the lower cover plate to cover the reference microchannel 301 and the measurement microchannel 302 to form a reference closed microchannel 311 and a measurement closed microchannel 312 .

[0098] The above-mentioned preparation of the micro thermal conductivity detector with an on-chip Wheatstone bridge can adopt this method, but is not limited to this. Figure 6 to Figure 10 , the preparation of the micro thermal conductivity detector in this embodiment is further introduced.

[0099] First, see Figure 5 and Figure 6 , execute step S1, provide a substrate.

[0100] Specifically, in this embodiment, the substrate adopts a silicon substrate 100, but is not limited thereto. The substrate may be replaced with a silicon-on-insulator substrate, a ceramic substrate or a glass substrate as needed. There is no excessive restriction on the selection of the material and size of the substrate.

[0101] Next, see Figures 5 to 9, performing step S2, forming a thermistor 400, a conductive connector and a support structure on the substrate, wherein the thermistor 400 includes a first thermistor 401, a second thermistor 402, a third thermistor 403 and a fourth thermistor 404, wherein the conductive connector connects the thermistors 400 to form a Wheatstone bridge, and the conductive connector includes an insulated first lead 501, a second lead 502 and a stacked cross-wire structure 503, wherein the first lead 501 connects the first thermistor 401 and the second thermistor 402, the third thermistor 403 and the fourth thermistor 404, The second thermistor 402, the second lead 502 connects the third thermistor 503 and the fourth thermistor 504, the stacked jumper structure 503 includes a stacked first insulation layer 543, a bottom lead 513, a second insulation layer 523 and a top jumper 533 from bottom to top, and the bottom lead 513 connects the first thermistor 401 and the third thermistor 403, and the top jumper 533 penetrates the second insulation layer 523 to connect the second thermistor 402 and the fourth thermistor 404.

[0102] In this embodiment, the support structure may include a first dielectric layer 601 and a second dielectric layer 602 stacked from bottom to top, and the thermistor 400 is located between the first dielectric layer 601 and the second dielectric layer 602. The preparation steps may include:

[0103] First, if Figure 6 , a silicon oxide layer 110 is first formed on the upper surface of the silicon substrate 100 .

[0104] Then, if Figure 7 After photolithography, the exposed silicon oxide layer 110 is removed by using a buffered oxide etchant (BOE) to remove the glue, and the silicon oxide layer 110 is used as a mask to etch the exposed silicon substrate 100 by using a KOH etchant to form a substrate receiving groove 120, so as to provide a receiving space for the supporting structure and the conductive connecting member prepared subsequently, so as to facilitate the subsequent bonding, but it is not limited to this. For example, a cover plate receiving groove 211 having a receiving structure and a conductive connecting member may be formed only in the subsequent upper cover plate, or corresponding receiving grooves may be formed in both the silicon substrate 100 and the upper cover plate, and no excessive limitation is made here.

[0105] Then, if Figure 7 After removing the mask formed by the silicon oxide layer 110, the first dielectric layer 601 is prepared on the upper surface of the silicon substrate 100, such as a stack of silicon oxide (SiOx) layers and silicon nitride (SiNx) layers or a single silicon oxide layer or silicon nitride layer.

[0106] Then, if Figure 8, the thermistor 400 is formed on the first dielectric layer 601, wherein the method for forming the thermistor 400 may be a sputtering method, such as preparing one of a Pt / Ti stack, a Ni / Cr stack, a W / Ti stack and a W / Re stack as the thermistor 400, and after photolithography, an ion beam etching process (IBE) is used to pattern the thermistor 400 to prepare the required thermistors 400, namely, the first thermistor 401, the second thermistor 402, the third thermistor 403 and the fourth thermistor 404.

[0107] In this embodiment, while preparing the thermistor 400, the first lead 501, the second lead 502, the bottom lead 513 and the pad 504 in the conductive connector are prepared to reduce the process steps, wherein the electrical connection components in the conductive connector are preferably made of the same material as the thermistor 400, that is, the first lead 501, the second lead 502, the bottom lead 513, the pad 504 and the subsequently prepared top crossover 533 include one of a Pt / Ti stack, a Ni / Cr stack, a W / Ti stack and a W / Re stack.

[0108] The conductive connector connects the thermistor 400 to form a Wheatstone bridge. Since the conductive connector is integrated into the substrate, it can replace external leads for electrical connection, thereby reducing the formation of contact resistance and reducing noise interference of the detector.

[0109] Then, if Figure 8 The second dielectric layer 602 , such as a stack of silicon oxide (SiOx) and silicon nitride (SiNx) layers or a single silicon oxide layer or silicon nitride layer, is prepared on the surface of the thermistor 400 to protect the thermistor 400 .

[0110] Next, photolithography is performed, and the second dielectric layer 602, i.e., the second insulating layer 523 is etched by reactive ion etching (RIE) to form a through hole, and then a sputtering method is used to form a metal layer of the top jumper 533, and then photolithography is performed and then an IBE process is used to etch to form a patterned top jumper 533 to achieve on-chip connection of the Wheatstone bridge.

[0111] Then, if Fig. 9, photolithography is performed, and RIE can be used to etch the second dielectric layer 602 and the first dielectric layer 601 to remove the dielectric layer in the bonding area and the pad 504 area to facilitate the subsequent bonding process, and to expose the pad 504 to facilitate the subsequent packaging welding, and to etch the dielectric layer located inside the support structure to form the support structure with a mesh structure, so as to increase the contact area between the support structure and the sample and increase the sensitivity.

[0112] Next, see Figure 5 and Fig.10 , execute step S3, provide an upper cover plate, and bond the upper cover plate to the upper surface of the substrate.

[0113] In this embodiment, the upper cover plate adopts a glass upper cover plate 210, but it is not limited to this. For example, the upper cover plate can also adopt an insulator silicon upper cover plate, a ceramic upper cover plate or a silicon upper cover plate, etc. There is no excessive restriction on the selection of the material and size of the upper cover plate. The glass upper cover plate 210 and the silicon substrate 100 can be anodic bonded. In this embodiment, the upper cover plate adopts a cover plate having the cover plate receiving groove 211, but it is not limited to this.

[0114] Next, see Figure 5 and Fig.10 , execute step S4, pattern the substrate from the lower surface of the substrate to form a reference microchannel 301 and a measuring microchannel 302, the first lead 501, the second lead 502 and the stacked cross-wire structure 503 are located on the substrate between the reference microchannel 301 and the measuring microchannel 302, and the first thermistor 401 and the fourth thermistor 404 are suspended in the measuring microchannel 302 through the supporting structure and are arranged along the airflow direction, the second thermistor 402 and the third thermistor 403 are suspended in the reference microchannel 301 through the supporting structure and are arranged along the airflow direction.

[0115] Specifically, photolithography is performed from the back side of the silicon substrate 100, and the silicon substrate 100 can be etched by deep reactive ion etching (DRIE) to form the reference microchannel 301 and the measurement microchannel 302 to release the support structure, so that the thermistor 400 is suspended in the microchannel through the support structure.

[0116] Next, see Figure 5 and Fig.10, execute step S5, provide a lower cover plate, and bond the lower cover plate to the lower surface of the substrate, combine the upper cover plate and the lower cover plate to cover the reference microchannel 301 and the measurement microchannel 302 to form a reference closed microchannel 311 and a measurement closed microchannel 312.

[0117] In this embodiment, the lower cover plate is a glass lower cover plate 220, but it is not limited thereto. For example, the lower cover plate may also be a silicon-on-insulator lower cover plate, a ceramic lower cover plate, or a silicon lower cover plate, etc. There is no excessive restriction on the material and size of the lower cover plate. The glass lower cover plate 220 and the silicon substrate 100 may be anodic bonded.

[0118] Finally, slicing and packaging steps may be performed to complete the preparation of the micro thermal conductivity detector.

[0119] Embodiment 2

[0120] See also Figure 11 to Figure 13 This embodiment also provides another micro thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon substrate and a preparation method thereof. The preparation of the micro thermal conductivity detector described above can adopt this method, but is not limited thereto. The main difference between this embodiment and the first embodiment is: See Fig.13 , a cover plate is only provided on one side of the substrate to form a closed microchannel, so as to reduce the number of cover plates used.

[0121] The preparation method of the micro thermal conductivity detector may include the following steps:

[0122] S1: Provide substrate;

[0123] S2: forming a thermistor 400, a conductive connector and a supporting structure on the substrate, wherein the thermistor 400 includes a first thermistor 401, a second thermistor 402, a third thermistor 403 and a fourth thermistor 404, wherein the conductive connector connects the thermistors 400 to form a Wheatstone bridge, and the conductive connector includes an insulated first lead 501, a second lead 502 and a stacked crossover structure 503, wherein the first lead 501 connects the first thermistor 401 and the second thermistor 404. The second lead 502 connects the third thermistor 403 and the fourth thermistor 404, the stacked crossover structure 503 includes a first insulating layer 543, a bottom lead 513, a second insulating layer 523 and a top crossover 533 stacked from bottom to top, and the bottom lead 513 connects the first thermistor 401 and the third thermistor 403, and the top crossover 533 penetrates the second insulating layer 523 to connect the second thermistor 402 and the fourth thermistor 404;

[0124] S3: Patterning the substrate to form a reference microchannel 301 and a measuring microchannel 302 with the bottom located in the substrate, the first lead 501, the second lead 502 and the stacked cross-wire structure 503 are located on the substrate between the reference microchannel 301 and the measuring microchannel 302, and the first thermistor 401 and the fourth thermistor 404 are suspended in the measuring microchannel 302 through the supporting structure and are arranged along the airflow direction, and the second thermistor 402 and the third thermistor 403 are suspended in the reference microchannel 301 through the supporting structure and are arranged along the airflow direction;

[0125] S4: providing an upper cover plate and bonding the upper cover plate to the upper surface of the substrate, and covering the reference microchannel 301 and the measurement microchannel 302 with the upper cover plate to form a reference closed microchannel 311 and a measurement closed microchannel 312 .

[0126] The types of the substrate and the cover in the micro thermal conductivity detector are not limited here, and can refer to the first embodiment. The preparation steps S1 and S2 of the micro thermal conductivity detector can refer to the first embodiment. Figure 6 to Figure 9 The preparation is not described in detail here, and only the distinction between step S3 and step S4 is described below.

[0127] Specifically, Fig.11 and Fig.12 , perform step S3, after forming the support structure, directly use a wet etching solution such as TMAH or KOH, or use SF 6 or XeF 2 A dry etching agent is used to remove the portion of the silicon substrate 100 located below the support structure to release the support structure and form the reference microchannel 301 and the measurement microchannel 302; or Fig.12 As shown, photolithography is used to first etch the silicon substrate 100 to a certain depth using a DRIE process, and then after degumming, a wet etching solution such as TMAH or KOH is used, or a SF 6 or XeF 2 A dry etching agent is used to remove a portion of the silicon substrate 100 located below the support structure to release the support structure.

[0128] Then, if Fig.11 and Fig.13 , executing step S4, bonding the glass cover plate 210 and the silicon substrate 100 by using anodic bonding, for example.

[0129] Finally, the steps of dicing and packaging can be performed to complete the preparation of the micro thermal conductivity detector with an on-chip Wheatstone bridge.

[0130] Embodiment 3

[0131] See also Figure 14 to Figure 18 This embodiment also provides a micro thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon-on-insulator substrate and a preparation method thereof. The preparation of the micro thermal conductivity detector mentioned above can adopt this method, but is not limited to this. The difference between this embodiment and the first embodiment is mainly that: the substrate adopts a silicon-on-insulator substrate 111 with a bottom silicon 101, a buried oxide layer 102 and a top silicon 103. For the micro thermal conductivity detector and the preparation method thereof, please refer to the first embodiment, which will not be described in detail here. Only the differences are described below.

[0132] Compared with the first embodiment, after the support structure is etched by RIE process, the top silicon 103 is etched by DRIE photolithography, and then the exposed buried oxide layer 102 is etched by RIE process; then the upper cover plate is bonded to the top silicon 103 of the silicon-on-insulator substrate 111; then photolithography and etching are performed from the lower surface of the silicon-on-insulator substrate 111 to form the reference microchannel 301 and the measurement microchannel 302 to release the support structure; then the lower cover plate is bonded to the silicon-on-insulator substrate 111; and the preparation of the micro thermal conductivity detector is completed by slicing and packaging.

[0133] Embodiment 4

[0134] See also Figure 19 to Figure 21 This embodiment also provides another micro thermal conductivity detector with an on-chip Wheatstone bridge based on a silicon-on-insulator substrate and a preparation method thereof. The preparation of the micro thermal conductivity detector mentioned above can adopt this method, but is not limited to this. The difference between this embodiment and the first embodiment is mainly that: the substrate adopts a silicon-on-insulator substrate 111 with a bottom silicon 101, a buried oxide layer 102 and a top silicon 103. For the micro thermal conductivity detector and the preparation method thereof, please refer to the first embodiment, which will not be described here. Only the differences are described below.

[0135] Compared with the first embodiment, in this embodiment, after the second dielectric layer 602 and the first dielectric layer 601 are etched by RIE process in photolithography, the top silicon 103 can be etched by DRIE process after photolithography again, and then the exposed buried oxide layer 102 can be etched by RIE process. Fig.19 ; Then deposit a protective layer 700, such as a SiNx layer and a SiOx layer or a stacked layer, to protect the sidewalls of the thermistor 400 and the top silicon 103; after photolithography, use the RIE process to etch the dielectric layer in the gap of the thermistor 400, and then use the DRIE process to etch the bottom silicon 101 to a certain depth, such as Fig. 20 ; Then use a wet etching solution such as TMAH or KOH, or use SF 6 or XeF2 A dry etching agent is used to remove a portion of the bottom silicon 101 located below the support structure to release the support structure, such as Fig.21 ; Etch the top silicon 103 bonding area, the pad 504 area, the second dielectric layer 602 area and the protective layer 700 of the top crossover 533 area by RIE process to facilitate bonding and electrical connection, and then bond the top cover plate and the top silicon 103 by anodic bonding, as shown in FIG. Fig.21 ; Finally, the preparation of the micro thermal conductivity detector with an on-chip Wheatstone bridge is completed by dicing and packaging.

[0136] In summary, the micro-thermal conductivity detector with an on-chip Wheatstone bridge and the preparation method thereof of the present invention integrates a conductive connector in the substrate to replace the external leads, thereby reducing the contact resistance generated by the external leads, reducing the noise interference of the detector, and improving the signal-to-noise ratio of the detector, thereby reducing the detection limit of the detector, and only provides four pad interfaces to the outside, which is convenient for the use of the device.

[0137] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A micro thermal conductivity detector with an on-chip Wheatstone bridge, characterized in that: The micro thermal conductivity detector comprises: A substrate, wherein a reference microchannel and a measurement microchannel are disposed in the substrate; Thermistors, the thermistors comprising a first thermistor and a fourth thermistor suspended in the measuring microchannel through a supporting structure and arranged along the airflow direction, and a second thermistor and a third thermistor suspended in the reference microchannel through the supporting structure and arranged along the airflow direction; A conductive connector, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, wherein the conductive connector includes a first lead, a second lead, and a stacked crossover structure that are insulated and located on the substrate between the reference microchannel and the measurement microchannel, wherein the first lead connects the first thermistor and the second thermistor, and the second lead connects the third thermistor and the fourth thermistor, and the stacked crossover structure includes a first insulating layer, a bottom lead, a second insulating layer, and a top crossover from bottom to top, wherein the bottom lead connects the first thermistor and the third thermistor, and the top crossover penetrates the second insulating layer to connect the second thermistor and the fourth thermistor; A cover plate is bonded to the substrate, and the reference microchannel and the measuring microchannel are covered by the cover plate to form a reference closed microchannel and a measuring closed microchannel.

2. The micro thermal conductivity detector according to claim 1, characterized in that: The support structure is in a mesh shape; the support structure includes a first dielectric layer located on the lower surface of the thermistor and a second dielectric layer located on the upper surface of the thermistor.

3. The micro thermal conductivity detector according to claim 1, characterized in that: The pads in the conductive connecting member are exposed on the cover plate.

4. The micro thermal conductivity detector according to claim 1, characterized in that: The cover plate is arranged on two opposite sides of the base plate, or the cover plate is arranged on only one side of the base plate; a cover plate receiving groove is arranged on one side of the cover plate adjacent to the base plate.

5. The micro thermal conductivity detector according to claim 1, characterized in that: The substrate includes a silicon substrate, a silicon-on-insulator substrate, a ceramic substrate or a glass substrate; the cover includes a silicon cover, a silicon-on-insulator cover, a ceramic cover or a glass cover.

6. A method for preparing a micro thermal conductivity detector with an on-chip Wheatstone bridge, characterized in that: The following steps are involved: providing a substrate; Thermistors, conductive connectors and supporting structures are formed on the substrate, wherein the thermistors include a first thermistor, a second thermistor, a third thermistor and a fourth thermistor, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, the conductive connector includes an insulated first lead, a second lead and a stacked crossover structure, the first lead connects the first thermistor and the second thermistor, the second lead connects the third thermistor and the fourth thermistor, the stacked crossover structure includes a stacked first insulating layer, a bottom lead, a second insulating layer and a top crossover from bottom to top, the bottom lead connects the first thermistor and the third thermistor, the top crossover penetrates the second insulating layer and connects the second thermistor and the fourth thermistor; Providing an upper cover plate, and bonding the upper cover plate to the upper surface of the substrate; The substrate is patterned from the lower surface of the substrate to form a reference microchannel and a measuring microchannel, the first lead, the second lead and the stacked cross-wire structure are located on the substrate between the reference microchannel and the measuring microchannel, and the first thermistor and the fourth thermistor are suspended in the measuring microchannel through the support structure and arranged along the airflow direction, and the second thermistor and the third thermistor are suspended in the reference microchannel through the support structure and arranged along the airflow direction; A lower cover plate is provided and bonded to the lower surface of the substrate, and the upper cover plate and the lower cover plate are combined to cover the reference microchannel and the measurement microchannel to form a reference closed microchannel and a measurement closed microchannel.

7. A method for preparing a micro thermal conductivity detector with an on-chip Wheatstone bridge, characterized in that: The following steps are involved: providing a substrate; Thermistors, conductive connectors and supporting structures are formed on the substrate, wherein the thermistors include a first thermistor, a second thermistor, a third thermistor and a fourth thermistor, wherein the conductive connector connects the thermistors to form a Wheatstone bridge, the conductive connector includes an insulated first lead, a second lead and a stacked crossover structure, the first lead connects the first thermistor and the second thermistor, the second lead connects the third thermistor and the fourth thermistor, the stacked crossover structure includes a stacked first insulating layer, a bottom lead, a second insulating layer and a top crossover from bottom to top, the bottom lead connects the first thermistor and the third thermistor, the top crossover penetrates the second insulating layer and connects the second thermistor and the fourth thermistor; The substrate is patterned to form a reference microchannel and a measuring microchannel with the bottom located in the substrate, the first lead, the second lead and the stacked cross-wire structure are located on the substrate between the reference microchannel and the measuring microchannel, and the first thermistor and the fourth thermistor are suspended in the measuring microchannel through the support structure and arranged along the airflow direction, and the second thermistor and the third thermistor are suspended in the reference microchannel through the support structure and arranged along the airflow direction; An upper cover plate is provided and bonded to the upper surface of the substrate, and the reference microchannel and the measurement microchannel are covered by the upper cover plate to form a reference closed microchannel and a measurement closed microchannel.

8. The method for preparing the micro thermal conductivity detector according to claim 6 or 7, characterized in that: During bonding, the substrate has a substrate receiving groove, and / or the upper cover has a cover plate receiving groove.

9. The method for preparing the micro thermal conductivity detector according to claim 6 or 7, characterized in that: The formed support structure is a mesh structure.

10. The method for preparing the micro thermal conductivity detector according to claim 6 or 7, characterized in that: The first lead, the second lead, the bottom lead and the pad are prepared while preparing the thermistor; the pad is exposed on the upper cover plate.

Images