DUAL RANGE PRESSURE SENSOR

[ 1 ] FIELD OF INVENTION

[2] The present invention relates to a pressure sensor having wide range of sensitivity.

[3] BACKGROUND OF THE INVENTION

[4] MEMS/NEMS-based pressure sensor has advantages in terms of their higher sensitivity, fast response time, robustness, reliability and size. In view of that, various MEMS/NEMS-based pressure sensor has been developed and commonly deployed for applications in automotive, industrial, medical and consumer products at recent time. The most common type of MEMS/NEMS-based pressure sensor is the diaphragm-type in which the diaphragm in the form of a square or circle is suspended at it edges to form a mechanical structure which would deform upon detection or application of external pressure. The pressure sensors are generally designed to cater for a specific pressure range as the sensing depends upon the physical dimension of the mechanical deforming structure, which is the diaphragm itself, and the sensing materials as it would govern the sensing characteristics of the sensors such as sensitivity and resolution. This impedes the versatility of the sensors as it would not be able to serve wide range of applications. Under normal circumstances, multiple pressure sensors would need to be utilised together in order to sense external pressure of different range.

[5] It is evident that in most resistive-based MEMS/NEMS pressure sensor design, the pressure sensing capabilities are limited to only a single pressure range and sensitivity response to cater for a particular application hence limiting the versatility and capabilities of the sensors to be utilised for various applications at one instance. One of the example is in EP 0619477, which discloses that in a pressure sensor whose sensi- tiveelement is constituted by a deformable membrane (22) carrying a bridge of piezoresistive strain gauges suitable for measuring deformation of the membrane, a decoupling piece (34) is interposed between the membrane (22) and its support (28). The decoupling piece includes a deformable zone (38), and limited clearance (44) is left between the outer peripheral zone (36) of the decoupling piece (34) and the support (28) such that when pressure is applied during manufacture of the sensor to fix the membrane (22) to the decoupling piece (34), e.g. by gluing, the deformable zone (38) does not break.At present, the pressure sensing range for resistive-based MEMS/ NEMS pressure sensor is limited due to the following: 1. The effect of the pressure sensing is based on the piezoresistive effect which is bounded to a lower range of pressure sensing sensitivity (0.1 to 0.3mV/V/kPa). Smaller change of pressure cannot be measured. 2. The pressure sensing range is focused solely on the middle edge of the diaphragm limiting the range of pressure detection. 3. There is no on chip-referenced pressure sensing measurement for accuracy verification and detection.

[6] SUMMARY OF THE INVENTION

[7] According to one aspect of the present invention, the present invention provides a pressure sensor (100) comprising:a substrate (100a) having an insulation layer (100b) on top of the substrate (100a); a diaphragm structure (100c) suspended at the substrate (100a); a piezoresistor (lOOd) located at the edges of the diaphragm (100c) for detecting low sensitivity pressure measurement; a pressure chamber (lOOe)below the diaphragm structure (100c) houses reference air pressure in the form of vacuumas reference pressure for pressure measurement; characterized in that a nanoresistive-based sensing material (lOOf) located on top of the diaphragm (100c) surface for detecting high sensitive pressure measurement.

[8] Above provision is advantageous as it overcomes the problems associated with

limited pressure range measurement due to the single low sensitivity sensing of the piezoresistor. This can be achieved by introducing another nanoresistive-based sensing material known to have high sensitivity towards pressure sensing. The nanoresistive- based sensing material would operate alongside CMOS-based piezoresistor on top of the diaphragm of the pressure sensor to ensure that both high and low sensitivity measurement of the pressure can be achieved. This in turn would enable a wider range of pressure sensing and allow operations of the pressure sensor in various types of applications; ranging from the less sensitivity stringent application of environmental pressure measurement to the higher pressure sensitivity medical applications for blood pressure measurement. In addition, both the pressure sensors can be operated in tandem for on chip accuracy measurement and verification for the purpose of calibration or error-detection and compensation.

[9] BRIEF DESCRIPTION OF THE DRAWINGS

[10] Figure 1 illustrates a) cross section view b) top view of the pressure sensor of the present invention.

[11] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[12] The present invention describes a pressure sensor with wide sensing range for usage in multi-applications environment requiring different specifications of pressure range such as automotive, healthcare, biomedical, aquaculture and environmental monitoring. The present invention comprising:a substrate (100a) having an insulation layer (100b) on top of the substrate (100a); a diaphragm structure (100c) suspended at the substrate (100a); a piezoresistor (lOOd) located at the edges of the diaphragm (100c) for detecting low sensitivity pressure measurement; a pressure chamber (lOOe)below the diaphragm structure (100c) houses reference air pressure in the form of vacuumas reference pressure for pressure measurement; characterized in that a nano-resistive-based sensing material (lOOf) located on top of the diaphragm (100c) surface for detecting high sensitive pressure measurement.

[13] The present invention overcomes the aforementioned issue by introducing a pressure sensor design which is capable of sensing the change of stress level in at least two different external applied pressure range of high (>100 kPa) and low (<100 kPa) on the same pressure sensor with the identical mechanical deforming diaphragm structure. A basic configuration of the present invention is shown in Figure la, b where there exists a diaphragm structure (100c) as the mechanical deforming structure which would deform upon application on external pressure. The piezoresistor (lOOd) and the nanoresistive-based sensing material (lOOf) located on top of the diaphragm surface for measuring the changes in the stress level upon deformation of the diaphragm. The pressure chamber (lOOe) located below the diaphragm structure (100c) houses the reference air pressure in the form of vacuum. The present invention is able to measure wide pressure sensing range on a single planar diaphragm-based pressure sensor device during operation.

[14] The working principle of the proposed device is that upon application of a high

external applied pressure on top of the diaphragm, the diaphragm (100c) of the pressure sensor (100) would deform resulting in the change of stress level within the diaphragm (100c). A conducting or semi-conducting material which forms a set of piezoresistors (lOOd) sit at the edges of the diaphragm (100c) to gauge the change in the intensity of the stress level within the diaphragm (100c) at a lower sensitivity through the consequent variation in the electrical resistant of the piezoresistor (lOOd). Similarly, the nanoresistive-based material (lOOf); due to the nature of its small morphology and feature size; is highly responsive to stress variation hence providing a higher sensitivity detection of the pressure variation. The change of the resistance detected through the sensing material would be translated into an electrical output that corresponds to the measured value of the applied pressure.

[15] Further explaining, at high change of stress level due to the high applied external pressure (>100kPa), there won't be meaningful electrical output from the nanoresistive- basedsensing material(lOOf) as it would exceed the measurable range due to its high sensitivity. Hence, only the electrical output from the piezoresistor (lOOd) would be captured. Likewise, upon application of a low external applied pressure on top of the diaphragm (100c), only the nanoresistive-basedsensing material(lOOf) would be able to measure the low change in the stress level of the diaphragm structure (100c). This enables the present invention to cater for applications of pressure sensing in wide range of pressure environment.

[16] The nanoresistive-based sensing material (lOOf) can be made of, but not limited to materials such as carbon nanotubes, or nanowires, or nanorods, or nanoparticles or nanofilm, or the like resistors. Although the invention has been described with reference to particular embodiment, it is to be understood that the embodiment is merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiment that other arrangements may be devised without departing from the scope of the present invention as defined by the appended claims.