Capacitance pressure sensor with S-type electrode for improved sensitivity

This paper aims at designing a differential pressure sensor. The objective of the work is to design and fabricate the electrodes of a capacitive pressure sensor, so as to measure absolute and differential pressure accurately with improved sensitivity. In place of conventional parallel plate diaphragm, S-type electrodes are proposed in the present work. The work comprises of study of the proposed design in terms of a mathematical model, input-output behavior along with detailed analysis of pressure distribution pattern. Output capacitance obtained for changes in pressure is converted to voltage with the suitable signal conditioning circuit and data acquisition system to acquire the signal on to a PC. A neural network model is designed to compensate the nonlinearities present in the sensor output. Input-output characteristics of the designed sensor shows an improved response as compared with existing pressure sensors.

Linearization of Characteristic Response of a Capacitive MEMS Pressure Sensor by Patterning the Dielectric Layer

The present work introduces a novel design that linearizes the characteristic capacitance-pressure (C-P) response of the pressure sensor in contact mode. The design relies on patterning the insulating (dielectric) layer that separates the two electrodes of the device when the device is in contact mode. Since the capacitance is inversely proportional to the gap between the electrodes and the dielectric constant of the insulating layer is several times more than that of air (or vacuum), the contact region of the two electrodes makes more significant contribution to the overall capacitance of the system. Therefore, if the dielectric layer is properly patterned, the shape of C-P response can be controlled. In this work, we focus on linearity of the sensor response, and design and optimize dielectric pattern to achieve the highest linearity. Finite element simulations are used to demonstrate the applicability of the design concept. Different sensor designs are modeled and simulated using ANSYS® Multiphysics solver and their responses are compared to that of a conventional capacitive pressure sensor. Coefficient of linear correlation between pressure and capacitance is used as a quantitative measure for improvement of linearity. The simulation results show that the linearity of the C-P response improves from 0.930 in a 600 μm-diameter conventional design to 0.978 for a sensor with patterned dielectric layer. Moreover, a smaller sensor with 300 μm diameter display linearity of 0.999 over a 1.25 MPa – 5.0 MPa pressure range.

Improving Linearity of Circular Capacitive Pressure Sensor by Using a Dimple Mask

A new design concept for MEMS capacitive pressure sensors is presented that can be used to improve the linearity of the capacitance-pressure (C-T) response of the sensor. The sensor uses an extra dimple mask and etching step in the fabrication process of the device to create small bumps under the pressure sensitive and flexible membrane. Different designs, including a conventional sensor, are modeled and simulated using FEM coupled-field multiphysics solver in ANSYS®. Polycrystalline silicon is used as the structural material in the simulations. Coefficient of linear correlation between device capacitance and ambient pressure is used as the linearity factor to quantitatively compare the performance of different sensors. The finite element analysis show that the linearity factor improves from 0.938 for a conventional design to 0.973 for a design with a central bump. For a design with five bumps (one at the center of membrane and four off-center) the linearity factor increases to 0.997 for bumps of 1.5 μm thickness for wide pressure range of 0.0–4.0 MPa. The proposed design can be tailored for different applications that require certain sensor materials or different pressure ranges by using optimized sensor dimensions.

Design of an Instrument for Liquid Level Measurement and Concentration Analysis Using Multisensor Data Fusion

This paper presents the design of an instrument for measuring the liquid level. The objective of this proposed work is to measure the level of liquid accurately even with variations in liquid concentration. The designed instrument should also be able to compute the concentration of additives in the liquid. For this purpose, a multisensor model comprising a capacitive level sensor (CLS), ultrasonic level sensor (ULS), and capacitance pressure sensor is used to acquire information of the liquid. The data acquired from all these sensors are processed using Pau’s multisensor data fusion framework to compute the level of liquid along with the concentration of additives added to the solution. Pau’s framework consists of alignment, association function, analysis, and representation functions. The designed multisensor technique is tested with real-life data for varying liquid levels and additives. The results obtained show that the successful implementation of the proposed objective producing a root mean square of percentage error is 1.1% over the full scale is possible.

A Capacitive MEMS Pressure Sensor With Wavy Membrane and Linear Capacitance-Pressure Response

A novel structure for capacitive MEMS pressure sensors is presented that can be used for a wide range of pressure sensing applications. The sensor is designed such that its characteristic capacitance-pressure (C-P) response is highly linear and could cover a wide range of working pressure. A capacitive pressure sensor includes two capacitive electrodes, one patterned on the substrate and the other one suspended creating a sealed cavity. The suspended electrode acts as the pressure sensitive membrane in the device and undergoes out-of-plane deformation when there is a change in ambient pressure, resulting in a change in the device’s capacitance. The design presented in this work uses a wavy-shape membrane with controlled deformations to provide a highly linear C-P response. The wavy shape of the membrane can be fabricated using grey-scale mask and lithography. ANSYS APDL multiphysics solver is used to model and simulate the pressure sensor and optimize its response. The material used in the design and simulations of the pressure sensor is silicon carbide making this design suitable for harsh environment applications. The simulation results show that if the size and the shape of the wave form in the membrane are optimized, highly linear C-P response can be achieved and also its working pressure range can be extended.

Embedded Seal Cavity Fabricated in HTCC MEMS Technology

This article presents a design and fabrication method of a embedded cavity using alumina casting-belt. This method is based on HTCC (high-temperature co-fired ceramic) MEMS technology with using fugitive materials. The test structures are fabricated using two different fugitive materialsPolyimide film and ESL4900 film and two different lamination pressures (15MPa and 21MPa). The final stack was sintered by selecting different temperature process parameters in the high-temperature sintering process. Complete the analysis of the sample cavity structure using a SEM (scanning electron microscope). The manufacturing method is available for structural integrity and good air tightness of ceramics sealed cavity and it will be applied to the fabrication of flow sensors, capacitance pressure sensors etc.