Vaisala PTB220 User Manual download pdf (Page 11)

CHAPTER 2___________________________________________________ PRODUCT DESCRIPTION

VAISALA __________________________________________________________________________ 5

Thin film metallization

Silicon

Vacuum gap

Silicon

Glass

Silicon diaphragm

FIGURE 2-1 The BAROCAP

pressure sensor

The BAROCAP

pressure sensor consists of two layers of single

crystal silicon having a layer of glass between them. The thinner

silicon layer is etched on both sides to create an integrated vacuum

reference chamber for the absolute pressure sensor and to form a

pressure sensitive silicon diaphragm. The thicker silicon layer is the

rigid base plate of the sensor and it is clad with a glass dielectric. The

thinner piece of silicon is electrostatically bonded to the glass surface

to form a strong and hermetic bond. Thin film metallization has been

deposited to form a capacitor electrode inside the vacuum reference

chamber; the other electrode is the pressure sensitive silicon

diaphragm.

The coefficients of thermal expansion of silicon and glass materials

used in the BAROCAP

pressure sensor are carefully matched

together in order to minimize the temperature dependence and to

maximize the long-term stability. The BAROCAP

pressure sensor is

designed to achieve zero temperature dependence at 1000 hPa and its

long-term stability has been maximized by thermal ageing at an

elevated temperature.

The BAROCAP

capacitive pressure sensor features a wide dynamic

range and no self-heating effect. The excellent hysteresis and

repeatability characteristics are based on the ideal spring

characteristics of single crystal silicon. In the BAROCAP

pressure

sensor, the silicon material is exerted to only few percent of its whole

elastic range.

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Vaisala PTB220 User Manual Page 11