Sensors

Various sensors are designed and fabricated at the Institute MNT, including light, force, pressure and flow sensors. Two examples of such sensors are shown here. 

Piezoresistive force and displacement sensor

Piezoresistive sensors are used in measuring force, displacement, pressure and strain. In this case, a piezoresistive sensor was integrated into a cantilever, in order to measure force and displacement. 

Principle

A piezoresistive sensor is a resistor, where the magnitude of the resistance changes with the effective mechanical strain on the material. When a cantilevers is bent, stess is induced which leads to a measurable change in the sensors resistance.

The cantilevers were fabricated using DRIE technology.

 

Typical Values

  • Cantilever width:          100 µm
  • Cantilever length:         800 µm
  • Cantilever thickness:    4 µm
  • Resistance:                  10 kΩ
  • Measurement range:    1 … 15 µN
Device
SEM image of cantilevers
Packaged device

Capacitive pressure sensor

Capacitive sensors are exceptionally well suited to the measurement of displacements and deflections of micro-components such as (cantilever) beams and membranes. In this case, the capacitive sensing principle was used to measure the displacement of a membrane. 

Principle

The capacitive pressure sensor is made up of two chambers, which are separated by a thin membrane. The membrane is fabricated on a silicon substrate using wet etching with KOH. Also on the silicon substrate, there is a glass substrate with metallization.

The membrane and the metal layer patterned on the glass constitute a parallel plate capacitor. When a differential pressure arises between the two chambers, the membrane bends. This displacement leads to a change in the capacitance of the sensor, which can then be measured electrically.

Typical Values

  • Membrane dimensions:                  12 x 12 mm
  • Membrane thickness:                     50 µm
  • Electrode spacing:                         14 µm
  • Capacitance:                                  100 … 190 pF
  • Measurement range (patm-pref):    0 … 1000 Pa
  • Resolution:                                     0.1 … 0.5 Pa

This sensor is fabricated as part of the Workshop Hands-on-MEMS.

Sensor as fabricated
Close-up image
Complete sensor system