A passive wireless gas sensor

Abstract

The application belongs to the technical field of passive wireless gas sensors, and discloses a passive wireless gas sensor, which comprises a silicon substrate layer, an upper dielectric layer and a lower dielectric layer arranged on the silicon substrate layer, and a polycrystalline silicon conductive layer arranged between the upper dielectric layer and the lower dielectric layer; the gas sensor further comprises a passive wireless gas-sensitive structure unit arranged above the upper dielectric layer and a passive wireless temperature control structure unit arranged below the silicon substrate layer; the passive wireless gas-sensitive structure unit and the passive wireless temperature control structure unit are electrically interconnected; the passive wireless gas-sensitive structure unit comprises a gas-sensitive signal reading coil and a gas-sensitive electrode unit; and the temperature control signal of the passive wireless temperature control structure unit is composed of a temperature control coil and an on-chip switch unit. The application improves the integration and stability of the structure of the gas sensor, has the function of passive wireless temperature control, and further simplifies the complexity of the temperature conditioning circuit; the passive wireless gas sensor has high sensitivity and good stability.

Description

Technical Field

[0001] This invention belongs to the field of passive wireless gas sensor technology, specifically relating to a passive wireless gas sensor. Background Technology

[0002] Gas sensors can be used to detect the levels of toxic gases in livestock sheds and greenhouses to determine whether manure needs to be removed, fertilizers applied, or ventilation required. Gas sensors serve as the data acquisition point and are a crucial component of the sensing layer in the agricultural and livestock IoT system. Miniaturization and intelligentization are the main directions of sensor development. Passive wireless micro-sensors, in particular, offer significant advantages in application and research value due to their flexible distribution, small size, and low power consumption.

[0003] Inductor-capacitor (LC) sensors primarily consist of an LC resonant circuit composed of a sensitive capacitor and a fixed inductor. The gas concentration sensitivity of the sensitive capacitor is determined by the gas-sensitive material that serves as its dielectric. Therefore, they offer advantages such as simple structure, ease of micromachining, low cost, and flexible structural design. However, research on LC gas sensors is relatively scarce. Most reported sensor inductor designs utilize PCB fabrication, which is detrimental to mass production and consistent manufacturing.

[0004] However, existing semiconductor gas sensors have problems such as low sensitivity at room temperature and significant temperature sensitivity, and generally require additional complex conditioning circuits to achieve temperature control during operation. Summary of the Invention

[0005] To address the technical shortcomings of existing gas sensors, such as low sensitivity and susceptibility to temperature fluctuations, this invention provides a passive wireless gas sensor. This sensor improves the integration and stability of the gas sensor structure, provides passive wireless temperature control functionality, and simplifies the complexity of the temperature conditioning circuit. The passive wireless gas sensor exhibits high sensitivity and good stability.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] This invention relates to a passive wireless gas sensor. The gas sensor includes a silicon substrate, on which an upper dielectric layer and a lower dielectric layer are disposed. A polysilicon conductive layer is disposed between the upper and lower dielectric layers. Through-holes are provided on the silicon substrate. The gas sensor also includes a passive wireless gas-sensitive structure unit disposed above the upper dielectric layer and a passive wireless temperature-control structure unit disposed below the silicon substrate. The passive wireless gas-sensitive structure unit and the passive wireless temperature-control structure unit are electrically interconnected. The passive wireless gas-sensitive structure unit includes a gas-sensitive signal reading coil and a gas-sensitive electrode unit. The temperature control signal of the passive wireless temperature-control structure unit is composed of a temperature-control coil and an on-chip switch unit. The on-chip switch realizes the connection and disconnection of the gas-sensitive signal reading coil and the temperature-control coil. The gas-sensitive signal of the passive wireless gas-sensitive structure unit... The reading unit consists of a gas-sensitive signal reading coil and a gas-sensitive electrode unit, forming an inductor-capacitor series resonant structure through a polysilicon conductive layer. The gas-sensitive signal reading coil is an on-chip planar spiral inductor coil, including a gas-sensitive signal reading coil body and a capacitor multiplexed electrode. The gas-sensitive electrode unit is an interdigitated capacitor structure with a gas-sensitive layer, including an upper interdigitated capacitor electrode and a lower interdigitated capacitor electrode. The upper interdigitated capacitor electrode is connected to the on-chip switch through metal in a via. Two vias are provided on the silicon substrate, filled with a first metal and a second metal respectively, and the filling is achieved through through-silicon via (TSV) technology. The first metal fills the space between the gas-sensitive signal reading coil and the temperature control coil, and the second metal fills the space between the upper interdigitated capacitor electrode and the cascaded moving beam of the on-chip switch.

[0008] A further improvement of the present invention is that: the gas-sensitive signal reading coil is an on-chip planar spiral inductor coil, and the upper interdigital capacitor electrode and the lower interdigital capacitor electrode are processed by metal electroplating process, and the material of the gas-sensitive electrode unit is graphene.

[0009] A further improvement of the present invention is that the temperature control coil is designed as a circular temperature control coil structure in the positive direction, and has a planar spiral inductor structure. The temperature control coil includes a temperature control coil body and a coil contact end.

[0010] The beneficial effects of this invention are:

[0011] (1) The gas-sensitive structural unit of the gas sensor of the present invention is processed by metal electroplating, which is small in size, highly integrated, has good consistency and good stability.

[0012] (2) The temperature control structure unit of the gas sensor of the present invention has the advantages of process compatibility, small size, simple conditioning circuit, wireless temperature control, and low total power consumption of the system.

[0013] (3) The gas-sensitive electrode unit of the gas sensor of the present invention adopts a functionalized graphene layer to achieve sensitivity to different types of gases.

[0014] (4) The temperature control coil and on-chip switch unit of the gas sensor of the present invention can be arrayed in multiple groups to realize a multi-temperature zone structure.

[0015] The gas sensor of this invention can achieve gas-sensitive signal reading and on-chip temperature control under different frequency signal control, thereby improving the gas sensitivity of the sensor. The consistent processing of the temperature control structure reduces the overall size of the device and has the advantages of process compatibility, simple conditioning circuit, and low power consumption. Attached Figure Description

[0016] Figure 1 This is a cross-sectional view of the passive wireless gas sensor of the present invention.

[0017] Figure 2 This is a top view of the passive wireless gas sensor of the present invention.

[0018] Figure 3 This is a top view of the passive wireless gas sensor of the present invention.

[0019] Figure 4 This is the equivalent circuit diagram of the passive wireless gas sensor of the present invention.

[0020] The components are as follows: 1. Silicon substrate layer; 2. Lower dielectric layer; 3. Polysilicon conductive layer; 3-1. Polysilicon lead structure; 3-2. Polysilicon contact electrode; 4. Upper dielectric layer; 5. Gas-sensitive signal reading coil; 5-1. Gas-sensitive signal reading coil body; 5-2. Capacitor multiplexing electrode; 6. Gas-sensitive electrode unit; 6-1. Upper interdigitated capacitor electrode; 6-2. Lower interdigitated capacitor electrode; 7-1. First metal; 7-2. Second metal; 8. Temperature control coil; 8-1. Temperature control coil body; 8-2. Coil contact terminal; 9. On-chip switch unit; 9-1. Support beam; 9-2. Pad; 9-3. Switch contact terminal; 9-4. Cascaded motion beam. Detailed Implementation

[0021] The embodiments of the present invention will be disclosed below with reference to the drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the present invention. That is, in some embodiments of the present invention, these practical details are not essential. In addition, for the sake of simplicity, some conventional structures and components will be shown in the drawings in a simple schematic manner.

[0022] like Figure 1As shown, this invention is a passive wireless gas sensor. The gas sensor includes a silicon substrate 1, on which an upper dielectric layer 4 and a lower dielectric layer 2 are disposed. A polycrystalline silicon conductive layer 3 is disposed between the upper dielectric layer 4 and the lower dielectric layer 2. Two vias are disposed on the silicon substrate 1, and the vias 7-1 and 7-2 are filled using through-silicon via (TSV) technology. The filling metal can be made of nickel, copper, or their alloys by electroplating, serving as a conductive material to achieve electrical connection between the upper and lower functional layers. The gas sensor also includes a passive wireless gas-sensitive structure unit disposed above the upper dielectric layer 4 and a passive wireless temperature control structure unit disposed below the silicon substrate 1. The passive wireless gas-sensitive structure unit and the passive wireless temperature control structure unit are electrically interconnected. The passive wireless gas-sensitive structure unit includes a gas-sensitive signal reading coil 5 and a gas-sensitive electrode unit 6. The temperature control signal of the passive wireless temperature control structure unit is composed of a temperature control coil 8 and an on-chip switching unit 9.

[0023] like Figure 2 As shown, the gas-sensitive signal reading unit of the passive wireless gas-sensitive structure unit is formed by the gas-sensitive signal reading coil 5 and the gas-sensitive electrode unit 6 through the polycrystalline silicon conductive layer 3 to form an inductor-capacitor series resonant structure. Both the gas-sensitive signal reading coil 5 and the gas-sensitive electrode unit 6 are made of metal electroplating, and the electroplating material can be metal copper, metal tungsten or metal nickel, etc.

[0024] The gas-sensitive electrode unit 6 is an interdigitated capacitor structure with a gas-sensitive layer. The gas-sensitive electrode unit 6 includes an upper interdigitated capacitor electrode 6-1 and a lower interdigitated capacitor electrode 6-2. The upper interdigitated capacitor electrode 6-1 is connected to the on-chip switch 9 through a second metal 7-2 in a through hole. The gas-sensitive signal reading coil 5 is an on-chip planar spiral inductor coil. The gas-sensitive signal reading coil 5 includes a gas-sensitive signal reading coil body 5-1 and a capacitor multiplexing electrode 5-2. The gas-sensitive signal reading coil 5 is an on-chip planar spiral inductor coil. The upper interdigitated capacitor electrode 6-1 and the lower interdigitated capacitor electrode 6-2 are both processed by metal electroplating. The material of the gas-sensitive electrode unit 6 is graphene grown epitaxially.

[0025] The capacitor multiplexing electrode 5-2 is the innermost inductor coil segment of the gas-sensitive signal reading coil body 5-1. The line width of the capacitor multiplexing electrode 5-2 is greater than the width of other coils in the gas-sensitive signal reading coil body 5-1. Its main function is to serve as both part of the coil and as a structural electrode of the lower interdigitated capacitor electrode 6-2, thereby realizing a serial connection structure between the capacitor structure of the gas-sensitive electrode unit 6 and the inductor coil structure of the gas-sensitive signal reading coil 5.

[0026] Appendix Figure 2The diagram shows the structure of the connection between the polysilicon conductive layer 3 and the gas-sensitive signal reading coil 5. The polysilicon conductive layer 3 is composed of a polysilicon lead structure 3-1 and a polysilicon contact electrode 3-2. The connection between the first metal 7-1 and the second metal 7-2 needs to be achieved through a via on the substrate.

[0027] like Figure 3 As shown, the temperature control coil 8 has a planar spiral inductor structure. The temperature control coil 8 includes a temperature control coil body 8-1 and a coil contact end 8-2. The coil contact end 8-2 is a part of the middle protrusion of the innermost inductor coil segment of the temperature control coil body 8-1. Its main function is to serve as both part of the coil and as a pair of switch electrode structures for the switch contact terminals 9-3.

[0028] The on-chip switch 9 includes a support beam 9-1, a pad 9-2, a switch contact terminal 9-3, and a cascaded motion beam 9-4. The support beam 9-1 is located at the head terminal of the cascaded motion beam 9-4. The deformation of the cascaded motion beam 9-4 will cause the support beam 9-1 to move horizontally, thereby enabling the switch contact terminal 9-3 at the front end of the support beam 9-1 to contact or disconnect with the coil contact terminal 8-2. The pad 9-2 is located at the tail terminal of the cascaded motion beam 9-4 and appears in pairs to support the cascaded motion beam 9-4. The contact and disconnection between the switch contact terminal 9-3 and the coil contact terminal 8-2 enables the connection and disconnection of the gas-sensitive signal reading coil 5 and the temperature control coil 8. The temperature control coil 8 is designed as a circular temperature control coil structure in the positive direction.

[0029] like Figure 3 and Figure 4 As shown, an alternating magnetic field is generated on the body 8-1 of the temperature control coil, which generates eddy currents through electromagnetic induction. Numerous eddy current loops heat the on-chip switch cascade moving beam 9-4, thereby causing the support beam 9-1 to move within the plane, which can realize the contact and disconnection of the switch contact terminal 9-3 and the coil contact terminal 8-2.

[0030] The gas sensor of the present invention is manufactured by the following method:

[0031] (1) Mark the silicon vias to be generated on the silicon substrate layer 1 with photoresist, etch blind holes on the silicon wafer by deep reactive ion etching, deposit titanium metal as a barrier layer and copper metal as a seed layer by chemical deposition, and fill the vias with copper metal by electroplating.

[0032] (2) The electroplated metal contact ends in the blind hole are exposed by chemical mechanical polishing and back grinding.

[0033] (3) A dielectric layer 2 is formed on the polished silicon wafer surface by sputtering, and photoresist is applied to the dielectric layer 2 and a polysilicon sputtering connection area is reserved through a mask.

[0034] (4) Deposit polysilicon and pattern the polysilicon to form the required lead connection layer.

[0035] (5) Deposit and pattern the upper dielectric layer 4 to protect the polysilicon. The upper dielectric layer can be silicon nitride and silicon oxide structure grown on the silicon nitride.

[0036] (6) Deposit and pattern the anchor area metal layer, using chromium and platinum in sequence, deposit the electroplating seed layer and pattern the metal layer, preferably copper and titanium.

[0037] (7) Spin-coating photoresist, photolithographically forming the metal layer structure of the front and rear functional structure regions, electroplating nickel to grow the functional structure, depositing and patterning the oxide layer to form the gas-sensitive structure processing area, performing reactive ion etching to expose the surface of the gas-sensitive structure layer, and generating the final gas-sensitive structure layer through the thermo-oxidation method.

[0038] (8) Remove the photoresist and release all metal functional structures.

[0039] This invention enables the reading of gas-sensitive signals and on-chip temperature control under different frequency signal control, thereby improving the gas sensitivity of the sensor. The consistent processing of the temperature control structure reduces the overall size of the device and has advantages such as process compatibility, simple conditioning circuit, and low power consumption.

[0040] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A passive wireless gas sensor, the gas sensor comprising a silicon substrate (1), an upper dielectric layer (4) and a lower dielectric layer (2) disposed on the silicon substrate (1), and a polycrystalline silicon conductive layer (3) disposed between the upper dielectric layer (4) and the lower dielectric layer (2), characterized in that: The silicon substrate (1) has through holes. The gas sensor also includes a passive wireless gas-sensitive structure unit disposed above the upper dielectric layer (4) and a passive wireless temperature control structure unit disposed below the silicon substrate (1). The passive wireless gas-sensitive structure unit is electrically interconnected with the passive wireless temperature control structure unit. The passive wireless gas-sensitive structure unit includes a gas-sensitive signal reading coil (5) and a gas-sensitive electrode unit (6). The temperature control signal of the passive wireless temperature control structure unit is composed of a temperature control coil (8) and an on-chip switch unit (9). The gas-sensitive signal reading coil (5) is an on-chip planar spiral inductor coil. The gas-sensitive signal reading coil (5) includes a gas-sensitive signal reading coil body (5-1) and a capacitor multiplexed electrode (5-2). The capacitor multiplexed electrode (5-2) is the innermost inductor coil segment of the gas-sensitive signal reading coil body (5-1). The line width of the capacitor multiplexed electrode (5-2) is greater than the width of other coils in the gas-sensitive signal reading coil body (5-1).

2. The passive wireless gas sensor according to claim 1, characterized in that: The passive wireless gas-sensitive structure unit's gas-sensitive signal reading unit is formed by the gas-sensitive signal reading coil (5) and the gas-sensitive electrode unit (6) through the polysilicon conductive layer (3) to form an inductor-capacitor series resonant structure, wherein the polysilicon conductive layer (3) is composed of a polysilicon lead structure (3-1) and a polysilicon contact electrode (3-2).

3. The passive wireless gas sensor according to claim 1, characterized in that: The gas-sensitive electrode unit (6) is an interdigitated capacitor structure with a gas-sensitive layer. The gas-sensitive electrode unit (6) includes an upper interdigitated capacitor electrode (6-1) and a lower interdigitated capacitor electrode (6-2). The upper interdigitated capacitor electrode (6-1) is connected to the on-chip switch unit (9) through a second metal (7-2) in a through hole.

4. The passive wireless gas sensor according to claim 3, characterized in that: The gas-sensitive signal reading coil (5) is an on-chip planar spiral inductor coil. The upper interdigital capacitor electrode (6-1) and the lower interdigital capacitor electrode (6-2) are both processed by metal electroplating. The gas-sensitive electrode unit (6) is made of graphene grown epitaxially.

5. A passive wireless gas sensor according to claim 4, characterized in that: The temperature control coil (8) has a planar spiral inductor structure. The temperature control coil (8) includes a temperature control coil body (8-1) and a coil contact end (8-2). The coil contact end (8-2) is a structure with a protrusion in the middle of the innermost inductor coil segment of the temperature control coil body (8-1).

6. The passive wireless gas sensor according to claim 5, characterized in that: The on-chip switch unit (9) includes a support beam (9-1), a pad (9-2), a switch contact terminal (9-3), and a cascaded motion beam (9-4). The support beam (9-1) is located at the head terminal of the cascaded motion beam (9-4). The deformation of the cascaded motion beam (9-4) will cause the support beam (9-1) to move horizontally, thereby enabling the switch contact terminal (9-3) at the front end of the support beam (9-1) to contact or disconnect with the coil contact terminal (8-2). The pad (9-2) is located at the tail terminal of the cascaded motion beam (9-4) and appears in pairs to support the cascaded motion beam (9-4). The contact and disconnection of the switch contact terminal (9-3) with the coil contact terminal (8-2) enables the connection and disconnection of the gas-sensitive signal reading coil (5) and the temperature control coil (8).

7. A passive wireless gas sensor according to claim 6, characterized in that: The silicon substrate (1) has two vias, and a first metal (7-1) and a second metal (7-2) are filled in the two vias. The vias are filled by through-silicon via (TSV) technology. The first metal (7-1) is filled to achieve electrical connection between the gas-sensitive signal reading coil (5) and the temperature control coil (8). The second metal (7-2) is filled to achieve electrical connection between the upper interdigital capacitor electrode (6-1) and the cascaded motion beam (9-4) of the on-chip switch unit (9).

8. The passive wireless gas sensor according to claim 7, characterized in that: The first metal (7-1) and the second metal (7-2) filling the through hole are nickel or copper.

9. A passive wireless gas sensor according to any one of claims 1-8, characterized in that: The temperature control coil (8) is designed as a circular temperature control coil structure in the positive direction.

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