SaM - MEMS Capacitive Pressure Sensor

Remeber:

• Capacitive Sensor are often used in MEMS devices to sense Pressure, this is the basic structure, with a fixed plate, and a deformable structure or membrane:
  
• ==In this case we have to suppose both the membrane and the fixed plate to be conductive and act as one of the plate of the sensor==.
• What our Sensor measures is the average of a differential preassure, specifically the preassure exerted on the membrane ($p_1$) and the pressure inside our sensor ($p_2$).
• What we obtain is a linear passive sensor with a formula like this:$C_0(1+x)$Where:
  • $C_0$ can assume values between $[???\frac{\text{?}}{\text{?}}÷???\frac{\text{?}}{\text{?}}]$.TODO
  • $x$ is a linear function of the differential preassure: $x=\alpha (P_1-P_2)$.
    It can assume values between $[???\frac{\text{?}}{\text{?}}÷???\frac{\text{?}}{\text{?}}]$.TODO

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Memory Card

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Capacitive Sensor are often used in MEMS devices to sense Pressure:

• As a primary sensor, the pressure can be sensed by means of a deformable plate or membrane.
  ==In this case we have to suppose the membrane to be conductive and act as one of the plate of the sensor==.
  Under the deformable conductive memebrane we have a conductive fixed plate.
• ==We measure the average of a differential preassure==.

• ${\overline{D}}_z$ : average of $D_z(r)$.
• $d_0$ : un-deformed distance between the two plates (constant).
• $\overline{d}$ : average distance.
  $\overline{d}=d_0(1-\frac{\overline{D_z}}{d_0})$
• $R$ : radius of the two circular plates.
• $r$ : our variable.
• ${\alpha }_D$: sensitivity.
• ${\alpha }_P=\frac{{\alpha }_D}{d_0}$: sensitivity.
• ==$x$ is a linear function of the pressure==: $x={\alpha }_P(P_1-P_2)$

Formulas used in the average integration:

1. Definition of average: $\overline{f}=\frac{1}{b-a}{\int }_a^{b}f(x)dx$
2. Change of Basis:$r\to {\rho }^2$
3. “Multiplied” the integral by:$\cdot \frac{\pi }{\pi }$