Piezoresistive sensor used in body

Abstract

An in-vivo piezoresistive sensor comprises a piezoresistive sensor chip, an insulating layer and a flexible flat cable. The piezoresistive sensor chip comprises a device substrate and a supporting substrate; the device substrate is arranged on the supporting substrate; a back cavity, a plurality of piezoresistive strips, a plurality of chip wires and a plurality of chip bonding pads are arranged on the device substrate; the piezoresistive strip and the chip bonding pad are electrically connected through a chip wire and form a Wheatstone bridge. The plurality of chip bonding pads are all positioned on the same side of the piezoresistive sensor chip; one end of the flexible flat cable is provided with a plurality of flat cable bonding pads in one-to-one correspondence with the chip bonding pads, and the other end of the flexible flat cable is provided with interface bonding pads in one-to-one correspondence with the flat cable bonding pads; the flexible flat cable is further provided with a plurality of flat cable wires, and the flat cable bonding pads and the interface bonding pads are connected one by one through the flat cable wires. The piezoresistive sensor chip and the flexible flat cable are welded through the chip bonding pad and the flat cable bonding pad; after welding, the interface bonding pad is outside the insulating layer, and the rest part of the flexible flat cable and the piezoresistive sensor chip are inside the insulating layer.

Description

Technical Field

[0001] This utility model belongs to the field of pressure sensors, specifically relating to an in vivo piezoresistive sensor that can be implanted in medical monitoring devices. Background Technology

[0002] MEMS (Micro-Electro-Mechanical Systems) piezoresistive sensors are miniature mechanical piezoresistive sensor chips applicable to medical, consumer electronics, and automotive electronics fields. Piezoresistive sensor chips convert piezoresistive signals into voltage signals using the Wheatstone bridge principle. Due to their simple fabrication process and excellent linearity, they are widely used. However, common piezoresistive sensor chips have signal lead pads located around the square sensitive membrane and lack biocompatibility. Therefore, when used in vivo (e.g., for monitoring intracranial pressure, fundus pressure), they result in large package sizes and higher packaging costs. Sensor probes made using these chips also require larger incisions during surgery, increasing surgical risks and hindering postoperative recovery. Therefore, optimizing the structure of pressure sensors to achieve biocompatibility while minimizing the surgical incision required for entry into the human body is a problem urgently needing to be solved by those skilled in the art. Utility Model Content

[0003] This invention aims to propose a piezoresistive sensor chip structure with pads distributed in the same direction and its associated flexible cable. The overall structure of the in vivo piezoresistive sensor formed by the two components is biocompatible, requiring only a small incision for insertion into the human body during surgery, and meeting various in vivo pressure monitoring needs.

[0004] The present invention employs the following solution: an in vivo piezoresistive sensor, comprising a piezoresistive sensor chip, an insulating layer, and a flexible cable; the piezoresistive sensor chip includes a device substrate and a supporting substrate; the device substrate is located on top of the supporting substrate; the device substrate has a back cavity, several piezoresistive strips, several chip wires, and several chip pads; the piezoresistive strips and chip pads are electrically connected through the chip wires to form a Wheatstone bridge; all the chip pads are located on the same side of the piezoresistive sensor chip; one end of the flexible cable has several cable pads corresponding one-to-one with the chip pads, and the other end has interface pads corresponding one-to-one with the cable pads; the flexible cable also has several cable wires, and the cable pads and interface pads are connected one-to-one through the cable wires; the piezoresistive sensor chip and the flexible cable are soldered through the chip pads and cable pads; after soldering, the interface pads are outside the insulating layer, and the remaining part of the flexible cable and the piezoresistive sensor chip are inside the insulating layer.

[0005] Existing micro piezoresistive sensors fabricated using MEMS technology typically have pads positioned around the perimeter of the sensor. The subsequent wire connections, together with the sensor itself, generally form a cylindrical shape, projecting as a circle in the direction of entry into the human body, requiring a relatively large surgical incision. If the sensor is to be inserted directly into the body from the side, wire bonding is necessary to pass some of the wires corresponding to the pads over the chip, creating wire crossings, increasing fabrication difficulty, and affecting the sensor's measurement stability. Furthermore, the pads surrounding the sensor increase the width of the sensor's side. This invention places the chip pads on the same side of the piezoresistive sensor chip, allowing direct connection to the entire flexible cable. After combining the piezoresistive sensor chip and flexible cable to form an in vivo piezoresistive sensor, its projected area in the direction of entry into the human body is only the cross-section of the piezoresistive sensor chip and flexible cable—a relatively thin rectangle—significantly reducing the surgical incision. Simultaneously, the in vivo piezoresistive sensor composed of the piezoresistive sensor chip and flexible cable is sheet-like, facilitating the encapsulation of an external biocompatible insulating layer and easily achieving better hermeticity.

[0006] Preferably, the supporting substrate material can be a single-crystal silicon substrate or a glass substrate.

[0007] Preferably, the device substrate can be a P-type single-crystal silicon substrate, an N-type single-crystal silicon substrate, or an SOI substrate.

[0008] Preferably, the cross-section of the back cavity can be trapezoidal or rectangular.

[0009] Preferably, the number of pads is 4 to 6. Generally, 4 pads are sufficient to complete the function of Wheatstone bridge in detecting pressure changes. More pads can be used to zero the pressure bar after the resistance value drifts, increasing the accuracy of pressure detection.

[0010] Preferably, the insulating layer material can be silicon oxide, silicon nitride, or other dielectric insulating materials.

[0011] Preferably, the chip pads, cable pads, and interface pads are coated with gold-silicon, gold-tin, or other biocompatible solders. Adding biocompatible solders ensures that even if the insulation layer is damaged during intra-articular work, the piezoresistive sensor used in the body will not cause harm to the human body, thus increasing the safety of this invention.

[0012] Preferably, the insulating layer material can be a biocompatible polymer such as Parylene, polyimide, medical epoxy resin, or polytetrafluoroethylene. Attached Figure Description

[0013] Figure 1 is a top view of the piezoresistive sensor chip of this utility model; Figure 2 is a top view of a conventional piezoresistive sensor chip; Figure 3 is a cross-sectional view of the piezoresistive sensor chip of this utility model; Figure 4 is a top view of the flexible ribbon cable of this utility model; Figure 5 is a cross-sectional view of the flexible ribbon cable of this utility model; Figure 6 is a structural diagram of the piezoresistive sensor chip of this utility model after being welded to the flexible ribbon cable.

[0014] In the figure: 1-piezoresistive sensor chip, 2-device substrate, 3-support substrate, 201-chip pad, 202-piezoresistive strip, 203-chip wire, 204-back cavity, 4-flexible cable, 401-cable pad, 402-interface pad, 403-cable wire. Detailed Implementation

[0015] Various exemplary embodiments, features, and aspects of this application will be described in detail below with reference to the accompanying drawings. The same reference numerals in the drawings denote elements with the same or similar functions. Although various aspects of the embodiments are shown in the drawings, they are not necessarily drawn to scale unless specifically indicated otherwise. Furthermore, several specific details are set forth in the following detailed description to better illustrate the present invention. Those skilled in the art will understand that the present application can be practiced without certain specific details. In some instances, methods, means, elements, and circuits well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present application.

[0016] Embodiment 1, as shown in Figures 1-3, illustrates that the piezoresistive sensor chip 1 of this invention includes a device substrate 2 and a supporting substrate 3. The device substrate 2 is located on top of the supporting substrate 3. The device substrate 2 has a back cavity 204, four piezoresistive strips 202, several chip wires 203, and four chip pads 201. The piezoresistive strips 202 and the chip pads 201 are electrically connected via the chip wires 203, forming a Wheatstone bridge. All four chip pads 201 are located on the same side of the piezoresistive sensor chip 1. The cross-section of the back cavity 204 is trapezoidal. Compared to existing miniature piezoresistive sensors, this invention has the advantage of allowing direct insertion into the human body with a thinner side, resulting in a smaller projected area in the insertion direction and a smaller required surgical incision. Existing miniature piezoresistive sensors require a large surgical incision if inserted into the human body from a top-down view; if inserted through a thinner side, wire bonding is necessary to pass some of the pads' corresponding wires through the top of the chip. This creates circuit crossings, increasing manufacturing difficulty, and also affects the sensor's measurement stability. Furthermore, the pads surrounding the sensor itself increase the width of the sensor's sides.

[0017] In Embodiment 2, as shown in Figures 4 and 5, the flexible ribbon cable 4 of this invention includes four ribbon cable pads 401 and four interface pads 402, which are connected one-to-one by ribbon cable conductors 403. The four ribbon cable pads 401 correspond one-to-one with the four chip pads 201 in Embodiment 1. This one-to-one correspondence between the four ribbon cable pads 401 and the four chip pads 201 facilitates mass production and welding using MEMS technology. The cross-sectional projection of the flexible ribbon cable 4 and the piezoresistive sensor chip 1 is both thin-film, allowing a portion of the flexible ribbon cable 4 to enter the human body without requiring additional surgical incisions. During operation, the interface pads 402 remain outside the body, connecting to other external devices.

[0018] In implementation method 3, as shown in Figure 6, after the piezoresistive sensor chip 1 is connected to the flexible ribbon cable 4, the whole structure is strip-shaped. After both are wrapped with a biocompatible insulating layer, the entire in vivo piezoresistive sensor can work safely inside the human body, and the surgical incision only needs to accommodate the thin sheet-like projected area to pass through.

[0019] The above description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A piezoresistive sensor for internal use, characterized in that, The device comprises a piezoresistive sensor chip, an insulating layer, and a flexible flat cable. The piezoresistive sensor chip includes a device substrate and a supporting substrate, with the device substrate situated on top of the supporting substrate. The device substrate has a back cavity, several piezoresistive strips, several chip wires, and several chip pads. The piezoresistive strips and chip pads are electrically connected via chip wires to form a Wheatstone bridge. All the chip pads are located on the same side of the piezoresistive sensor chip. One end of the flexible flat cable has several flat cable pads corresponding to the chip pads, and the other end has interface pads corresponding to the flat cable pads. The flexible flat cable also has several flat cable wires, and the flat cable pads and interface pads are connected one-to-one via the flat cable wires. The piezoresistive sensor chip and the flexible flat cable are soldered together via the chip pads and flat cable pads. After soldering, the interface pads are outside the insulating layer, while the remaining portion of the flexible flat cable and the piezoresistive sensor chip are inside the insulating layer.

2. The piezoresistive sensor for internal use according to claim 1, characterized in that, The supporting substrate material can be a single-crystal silicon substrate or a glass substrate.

3. The piezoresistive sensor for internal use according to claim 2, characterized in that, The device substrate can be a P-type single-crystal silicon substrate, an N-type single-crystal silicon substrate, or an SOI substrate.

4. The piezoresistive sensor for internal use according to claim 3, characterized in that, The cross-section of the back cavity can be trapezoidal or rectangular.

5. A piezoresistive sensor for internal use according to claim 4, characterized in that, The number of solder pads is 4 to 6.

6. A piezoresistive sensor for internal use according to claim 5, characterized in that, The insulating layer material can be silicon oxide or silicon nitride.

7. A piezoresistive sensor for internal use according to claim 6, characterized in that, The chip pads, cable pads, and interface pads are covered with gold silicon or gold tin solder.

8. A piezoresistive sensor for internal use according to claim 7, characterized in that, The insulating layer material can be Parylene, polyimide, medical epoxy resin, or polytetrafluoroethylene.

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