CN1651910A - Capacitive relative humidity sensor - Google Patents

Abstract

The present invention discloses a capacitive relative humidity sensor for microelectronic mechanical system. It is formed from substrate, capacitor upper polar plate and capacitor lower polar plate. Said capacitor lower polar plate is placed on the substrate, said capacitor upper polar plate is positioned over the capacitor lower polar plate, in the area outside of capacitor upper polar plate projection an oxide layer is set, and on the oxide layer the leads of capacitor upper polar plate and capacitor lower polar plate are set, and on the capacitor upper polar plate a humidity-sensing medium layer is set. Said invention has the advantage of providing deformation space for movable upper polar plate.

Description

Capacitive relative humidity sensor

Technical field

The invention relates to a relative humidity sensor, in particular to a capacitive relative humidity sensor of a micro-electromechanical system.

Background technique

Humidity measurement has important applications in industrial and agricultural production, meteorology, environmental protection, national defense, scientific research, aviation and other departments. As an important part of the humidity measurement system, the humidity sensor has been developed for many years. From the initial hair meter and dry wet bulb hygrometer to the LiCl electrolyte humidity sensor that can output electrical signals. Electrolyte humidity sensor, ceramic humidity sensor, semiconductor junction type and MOS type humidity sensor and emerging polymer humidity sensor appeared in the development process. The miniature humidity sensor based on MEMS technology has the characteristics of small size, low price and good product consistency, and it is a hot spot in the research of humidity sensors in recent years. In 1997, Buchhold proposed the use of MEMS technology to manufacture a piezoresistive humidity sensor. The humidity sensor is a movable sensitive film covered with a layer of hygroscopic polymer. When the external humidity changes, the polymer expands and contracts, thereby driving the movable sensor. The membrane deforms, which eventually causes the resistance value of the piezoresistor on the four sides of the membrane to change. The inherent large temperature drift characteristics of resistors have limitations in applications where the temperature changes greatly. In 2002, Chatzandroulis used the silicon micromachining process to manufacture a humidity sensor with a cantilever beam structure. The cantilever beam is covered with a hygroscopic material. When the hygroscopic material absorbs the ambient humidity, it expands and generates stress, and the weight increases, causing the cantilever beam to bend. The capacitance between the cantilever and the substrate changes. The sensor is capacitive, so the temperature drift is small, but because of the cantilever beam structure with one end fixed, the reliability is relatively poor, and the cantilever beam will warp to varying degrees due to the residual stress during the release process, resulting in poor product consistency. .

Contents of Invention

The invention provides a capacitive relative humidity sensor with small temperature drift for micro-electromechanical systems. The invention has the advantages of high sensitivity and good reliability at the same time.

The present invention adopts following technical scheme:

A capacitive relative humidity sensor for microelectromechanical systems, consisting of a substrate, a capacitor lower plate and a capacitor upper plate, the capacitor lower plate is arranged on the substrate, and the capacitor upper plate is located at the bottom of the capacitor On the top, an oxide layer is provided on the area other than the projection of the upper plate of the capacitor on the upper plate of the capacitor, the lead wires of the upper and lower plates of the capacitor are arranged on the oxide layer, and a moisture-sensitive medium layer is provided on the upper plate of the capacitor, which is characterized in that The upper plate of the capacitor is supported by four square anchor areas and connecting rods fixed on the oxide layer.

Compared with prior art, the present invention has following advantage:

The invention is a movable thin-film capacitive humidity sensor used for sensing environmental humidity signals, which consists of upper and lower capacitor plates and lead wires connecting the electrode plates. The upper plate of the capacitor is a movable film, the lower plate is a fixed electrode, and the upper plate is covered with a layer of hygroscopic material. When the ambient humidity changes, the hygroscopic material expands or contracts, thereby driving the deformation of the upper plate of the capacitor. This causes a change in capacitance value. A cavity is provided under the upper pole plate of the capacitor to provide a deformation space for the movable upper pole plate.

The invention can be manufactured by combining standard CMOS technology and MEMS processing technology, and has high precision and good long-term reliability. In the present invention, the cavity below the upper plate is formed by bonding technology, while generally adopting to deposit LTO (low temperature silicon dioxide) or PSG (phosphorus-doped silicon dioxide) as a sacrificial layer in the traditional process, and then Release the sacrificial layer to form a cavity. For a cavity with a relatively large area, this will often cause the released structure to stick to the bottom of the cavity, making the device invalid. The bonding technology used in the present invention will overcome this defect and greatly enhance the performance of the sensor. reliability. The upper plate is a movable film with four corners fixed, and the whole upper plate is supported by four fixed corners. Compared with the film with four fixed sides, its sensitivity is greatly improved, and the four sides of the movable film are suspended and do not contact the oxide layer. , which can effectively reduce the edge parasitic capacitance. The front end of the sensor adopts standard CMOS technology, and the back end adopts body processing technology, which does not affect the IC process processing of the front end. The compatibility of the IC process is guaranteed, which is beneficial to the mass production of the sensor. The processing of the back-end body is beneficial to enhance the reliability and strength of the movable film, and increasing the area of the movable film can effectively increase the variation of the humidity-sensitive capacitance. The capacitive humidity sensor manufactured based on the MEMS technology proposed by the present invention effectively improves sensitivity and reliability, has small temperature drift, and is suitable for high-precision measurement of environmental relative humidity.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

Figure 2 is a top view of the present invention.

Fig. 3 is a cross-sectional view of the present invention.

Detailed ways

A capacitive relative humidity sensor for microelectromechanical systems, consisting of a substrate 1, a capacitor lower plate 2 and a capacitor upper plate 5, the capacitor lower plate 2 is set on the substrate 1, and the capacitor upper plate 5 Located above the capacitor lower plate 2, an oxide layer 3 is provided on the capacitor upper plate 5 outside the projection of the capacitor upper plate 5, and the oxide layer 3 is provided with capacitor upper and lower plate leads 41, 42. The upper pole plate 5 is provided with a moisture-sensitive medium layer, and the upper pole plate 5 of the capacitor is fixed on the four square anchor areas on the oxide layer 3 through connecting rods. In this embodiment, the upper pole plate 5 of the capacitor is fixed on the four corners of the On the oxide layer 3, the moisture-sensitive medium layer is a polyimide layer. In this embodiment, the substrate 1 is bulk silicon, the lower electrode plate 2 of the capacitor is a heavily phosphorus-doped region, the oxide layer 3 is silicon dioxide, the upper electrode plate 5 of the capacitor is a heavily boron-doped region, and the upper and lower capacitor plate leads 41 and 42 is aluminum. The present invention can be made with following technology: prepare two silicon wafers 1# and 2#. For silicon wafer 1#, phosphorus ion implantation is carried out on the substrate 1 to form the lower plate 2 of the capacitor; a silicon dioxide layer 3 is deposited by CVD, and photolithography is performed on the oxide layer 3 to form a space for the movement of the upper plate of the capacitor. cavity and capacitor bottom plate lead through hole. Carry out boron ion implantation to silicon wafer 2#, form a conductive layer; Silicon wafer 1# is bonded with the surface of silicon wafer 2# boron ion implanted surface with corrosion pattern; Then silicon wafer 2# is polished by chemical mechanical polishing and Thinning by wet etching, and finally only the boron ion implantation layer is left; the upper plate 5 of the capacitor is formed by dry etching, the upper and lower plate leads 41 and 42 of the capacitor are formed by steaming aluminum and photolithography, and a Layer polyimide, and photolithographically form the moisture-sensitive medium layer 6, and finally imidize the polyimide. Due to changes in the relative humidity of the external environment, the moisture-sensing medium layer 6 of the present invention absorbs/desorbs moisture molecules in the air, causing the volume of the moisture-sensing medium layer 6 to expand or shrink, which drives the capacitor upper plate 5 to deform, and the capacitor The capacitance value between the upper plate 5 and the lower plate 2 of the capacitor changes, the relative humidity of the environment increases, the moisture-sensitive medium layer 6 absorbs water vapor molecules, the volume expansion drives the upper plate of the capacitor to bend downward, and the upper plate of the capacitor 5 and the capacitance value between the lower plate 2 of the capacitor increases.

Claims (3)

1. A capacitive relative humidity sensor for MEMS, consisting of a substrate (1), a capacitor lower plate (2) and a capacitor upper plate (5), the capacitor lower plate (2) is located at On the substrate (1), the capacitor upper plate (5) is located above the capacitor lower plate (2), and an oxide layer ( 3), the oxide layer (3) is provided with capacitor upper and lower plate leads (41, 42), and a moisture-sensitive medium layer is provided on the capacitor upper plate (5), which is characterized in that the capacitor upper plate (5) It is supported by four square anchor areas and connecting rods fixed on the oxide layer (3). 2. The capacitive relative humidity sensor according to claim 1, characterized in that the capacitive upper plate (5) is fixed to four square anchor areas on the oxide layer (3) through connecting rods. 3. The capacitive relative humidity sensor according to claim 1 or 2, characterized in that the moisture-sensing medium layer is a polyimide layer.

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