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MEM-CPS

 

> Micro-Electro-Mechanical Capacitive Pressure Sensor

 

MEM-CPS is an EDA solution to support designers in their development of capacitive pressure sensors for integration in an electronic circuit. It generates the layout of the mechanical part of pressure sensors and a suitable VHDL-AMS model for the electrical simulation of the pressure sensor with any (readout-) circuit. The sensor model is assembled from the EMBLEM-Mecha library. The full electromechanical system can thus be verified and optimized virtually.

The basic principle of the pressure device is that some external pressure deflects the upper plate of the sensor which results in a change io its capacitance, as detected by the readout circuit. The system behavior basically depends on the shape of the deflected upper plate, since it determines the pressure device capacitance. > User Interface Tool MICSTET The user interface based on command lines computes, from the geometrical dimensions, the contact pressure and the array capacitance at 0 bar, and conversely. It displays the sensor dimensions and generates a technical file for the VHDL-AMS model and a Job file for the layout generator. > Layout Generator PSGEN With the Job file in MICSTET, the Ada based layout generator creates the layout of the capacitive pressure sensor in GDSII format.

> Simulation Model

The analytic simulation model in VHDL-AMS runs on SMASH, with input parameters are in the data sheet, to allow fast and accurate simulation.
It treats the external pressure and the voltage between the electrical terminals. The voltage between the two plates induces an electrostatic force that in turn deflects the upper plate in addition to the external pressure. Moreover, the model describes the behavior of the poly-silicon membrane, especially when the membrane enters in contact with the substrate.

 

> MEM-CPS - VHDL-AMS model

> Symbol > Generic and Ports GENERIC Thickness Thickness of capacity plate QUANTITY P variable pressure input TERMINAL elec_p elec_n electrical out-/ input of the capacity > Simulation Example The waveform window shows in the first graph the two non overlapping clocks and in the second the rising pressure from 0 to 10 Bar (10.105Pa). The third graph displays the maximum deflection of the sensor and the reference plate. The fourth graph represents the capacitance of the two elements, and the last graph shows the output of the circuit.

> Variable Model Parameters > Modeled Sensor Structure The model of the capacitive pressure device consists in four independent parts: Deflection of the membrane under pressure and of the electrostatic force Electrostatic pressure computation of complete capacitance Electrical terminals