CN1851472A - Pressure-resistance athermal flow speed-direction sensor based micro mechanical technology - Google Patents

Abstract

Said Transducer utilizes piezoresistive doped quadrature supporting beam to proceed detection. Said transducer consists of upright post, quadrature supporting beam, and SOI silicon substrate, wherein said SOI silicon substrate being a hollow rectangle, quadrature supporting beam set on upper part of SOI silicon substrate, upright post set at intermediate crossing part of quadrature supporting beam, said upright post made from SU -8 glue. Said transducer has advantages of two dimension wind direction mensurability, small power consumption, fast responding, small temperature drift and fine reliability.

Description

Piezoresistive Athermal Flow Velocity and Direction Sensor Based on Micromechanical Technology

technical field

The invention relates to a micromechanical non-thermal flow velocity and flow direction sensor, in particular to a piezoresistive flow velocity and flow direction sensor which utilizes doped piezoresistive orthogonal support beams for detection.

Background technique

Fluid measurement has important applications in industrial and agricultural production, meteorology, environmental protection, national defense, scientific research, aviation and other departments. Among them, flow velocity and direction measurement, as an important part of fluid measurement, has been developed for many years. There have been measurement methods such as wind cup and vane measurement, pitot tube measurement, float measurement, mechanical measurement, acoustic measurement, optical measurement, heat transfer measurement, and electromagnetic measurement. The micro flow rate and flow direction sensor based on MEMS processing technology has the characteristics of small size, low price and good product consistency, and it has become a hot spot in the research of fluid sensors in recent years. Van Putten (personal name) proposed the first flow sensor based on silicon micromachining technology in 1974. The working principle of this sensor is based on heat transfer, that is, the flow rate and flow direction information is measured by measuring the thermal field change caused by fluid flow. After more than 30 years of development, thermal microfluidic sensors are now mainstream, especially in the field of anemometers. However, thermal microfluidic sensors also have their inherent disadvantages. For example, large power consumption, measurement errors due to thermal conduction of the substrate, zero point drift with ambient temperature, long response time, etc. In addition, because the fluid needs to be heated, the application of thermal microfluidic sensors in biology is limited. Athermal microfluidic sensors can overcome the above disadvantages. Kersjes (name) proposed a method for measuring differential pressure, Oosterbroek (name) proposed a method for measuring pressure drop, Svedin (name) proposed a method for measuring lift, and Ng (name) proposed a method for measuring viscous force. At present, the common disadvantages of flow velocity and direction sensors based on the non-thermal principle are the small measuring range and the inability to measure two-dimensional wind direction.

technical content

Technical problem: The purpose of this invention is to provide a piezoresistive non-thermal flow velocity sensor based on micromechanical technology, which has the advantages of measuring two-dimensional wind direction, low power consumption, fast response, small temperature drift and good reliability.

Technical solution: The present invention is a piezoresistive flow rate and direction sensor for measuring fluid flow velocity and flow direction signals, which is composed of four orthogonal support beams doped with piezoresistivity, a column above the beams and lead wires. The sensor is composed of a column, an orthogonal support beam, and an SOI silicon substrate. The SOI silicon substrate is a hollow rectangle, and an orthogonal support beam is arranged on the upper part of the hollow part of the SOI silicon substrate. There are columns.

When the sensor is in the fluid, the fluid flow generates pressure on the column, the direction of the pressure is the same as the flow direction, and the pressure depends on the flow rate. The uprights transmit the pressure to the orthogonal support beams, which are strained, producing stresses whose magnitude depends on the direction and velocity of the flow. By doping the piezoresistive on the beam, the stress on the beam is measured, so as to obtain the flow velocity and flow direction information, that is, the information of the two-dimensional flow direction is converted into the piezoresistive change output of the orthogonal support beam doped with piezoresistive.

Beneficial effects: the present invention can be manufactured by using MEMS processing technology, the manufacturing method and structure are very simple, and the reliability is good. Traditional thermal fluid sensors obtain flow velocity and flow direction information by setting heating components, allowing fluid to flow through the heating components, and measuring changes in the thermal field or temperature changes of the heating components. Due to the heating of the fluid, the power consumption is large and the temperature effect is obvious. The invention adopts the principle of mechanics to measure, and obtains the flow velocity and flow direction information by measuring the force of the fluid on the column. This defect is thereby avoided. Most traditional non-thermal fluid sensors use Bernoulli's principle to measure pressure difference or pressure drop, and cannot obtain two-dimensional direction information. The present invention sets orthogonal support beams to solve this problem, and can obtain two-dimensional direction information by detecting the stress changes of mutually orthogonal support beams. The pillars are made of SU-8 glue, which is a negative photoresist with half the density of silicon. The column is formed by developing with SU-8 glue, which can effectively reduce the weight of the column while ensuring the force-bearing area. The SU-8 glue is made into a ring, which can further reduce the weight of the column. SOI (silicon-on-insulator) silicon chips formed by bonding are used as structural materials, and movable cavities under the support beams are formed by backside etching and sacrificial layer release. In the traditional process, LTO (low temperature silicon dioxide) or PSG (phosphorus-doped silicon dioxide) is usually deposited as a sacrificial layer, and then the sacrificial layer is released to form a cavity. For a cavity with a relatively large area, this often causes The released structure adheres to the bottom of the cavity, making the device invalid. The SOI silicon chip technology adopted in the present invention will overcome this defect and greatly enhance the reliability of the sensor.

Description of drawings

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

Fig. 2 is a sectional view along A-A in Fig. 1 of the present invention.

In the above figure, there are column 1 , orthogonal support beam 2 , and SOI silicon substrate 3 .

Detailed ways

The invention is a fluid sensor for flow velocity and flow direction sensing, which is composed of SU-8 glue column 1 , doped piezoresistive orthogonal support beam 2 and SOI silicon substrate 3 . The SOI silicon substrate 3 is a hollow rectangle, and an orthogonal support beam 2 is arranged on the upper part of the hollow part of the SOI silicon substrate 3 , and a column 1 is arranged at the intersection of the middle of the orthogonal support beam 2 . The support beam is formed by isotropic etching on the back and ICP etching on the front. In this embodiment, the substrate is formed by bonding two single-crystal silicon wafers whose surfaces are oxidized, and the function of the oxide layer is to self-stop the anisotropic wet etching on the back side. Orthogonal support beams are obtained by etching monocrystalline silicon by ICP, on which piezoresistors are diffused and metal leads are sputtered. SU-8 adhesive posts were obtained by spin coating and developing. When the external fluid acts on the column 1, the column 1 will receive the same force as the flow direction, thus driving the support beam 2 to bend and twist, and produce different stress changes on each beam. This change is passed through the resistivity of the piezoresistor on the beam Changes are reflected. The substrate 3 is fixed and provides single-end support for the orthogonal beam 2 . Therefore, the information of flow velocity and flow direction can be obtained by measuring the change of piezoresistive resistivity on each orthogonal support beam.

The manufacturing process of the sensor in this example is: preparation of single crystal silicon wafers 1# and 2#; oxidizing and bonding 1# and 2# to form SOI substrate 3; anisotropic etching of backside 2# until the oxide layer self-stops; CMP ( chemical mechanical polishing) grinding plate 1# to make the thickness of the silicon layer on the oxide layer meet the needs of the support beam; front ICP etching 1# to form the orthogonal support beam 2; the silicon dioxide sacrificial layer is released; doping pressure on the support beam 2 Resist and wire; Spin and develop SU-8 glue to form column 1.

Claims (2)

1. A piezoresistive athermal flow rate sensor based on micromechanical technology, characterized in that the sensor is made up of a column (1), an orthogonal support beam (2), an SOI silicon substrate (3), and the SOI silicon substrate (3) is a hollow rectangle, an orthogonal support beam (2) is arranged on the upper part of the hollow part of the SOI silicon substrate (3), and a column (1) is arranged at the intersection of the middle of the orthogonal support beam (2). 2. The piezoresistive non-thermal flow rate sensor based on micromechanical technology according to claim 1, characterized in that the column is made of SU-8 glue.