pH Value Sensors

Design Options of a Conductivity Sensor

Chemical Sensing

In the area of chemical sensor technology, Fraunhofer IPMS develops sensors for the detection of ions, ionic conductivity and temperature in aqueous solutions as well as the presence of selected atmospheric gases.

  1. Sensors in liquid media:
    1. Ion-sensitive field-effect transistor (ISFET)
    2. Conductivity sensor
    3. Temperature sensor

  2. Gas sensors for environmental use and harsh air monitoring:
    1. Solid state gas sensor
    2. Ion mobility spectrometer (IMS)

Ion-sensitive Field-Effect Transistor (ISEFT)

  • Design and development of ISFET-chips and wafer test structures

  • Metrological examination and characterization at wafer level
    • Modeling of sensor operating point forecast
    • Layer characterization
    • Wafer area assessment
  • Development and design of structural and connection technologies for sensor use (modular concept)
    • Analyses and development for the polymeric-technical isolation of ISFET-chips
    • Assessment and testing of sensor seals
  • Metrological testing and characterization in aqueous solution (pH0-14, 0-95°C)
    • Development, testing and automation of measurement and characterization sequences
  • Production of ISFET-chips for the industry (main application area of food chemistry as half-cells in pH-sensors with conventional reference electrodes for extended use up to 135°C)

Conductivity Sensor

Quadrupole for capacitive and conductivity measurement methods: 

  • Design and development of CMOS-compatible conductivity sensor structures
  • Design and integration of the conductivity structure in the pH-sensor system
  • Metrological testing and characterization
  • Design and development of circuits for integrating the AC-conductivity sensor system in the DC-pH-sensor
     

Fields of application:

  • Environmental sensors
  • Water monitoring
  • Wastewater technology
  • Microfluidics
  • Sports medicine / body sensor system 
     

Characteristics:

  • Measurement range: 10µS/cm to 100mS/cm          
  • Cell constant: ca. 0,6 - 0,8 1/cm
  • Chip dimension: 5x5mm
     

Construction:

  • Si wafer with SiO2
  • Leads from Al + Tantalum
  • Passivation of the surface with tantalum pentoxide (Ta2O5)

Temperature Sensor

  • Design and development of CMOS-compatible temperature sensor structures and test structures
  • Metrological testing and characterization
  • Design and integration of the temperature sensor structure in the pH sensor and conductivity sensor
  • Design and development of circuits for integrating the temperature sensor system in the pH sensor/conductivity sensor

Ion Mobility Spectrometer (IMS)

  • Sensor materials: Bulk-Si
  • Detected substances: organic solvents (benzene, acetone, ethanol)
  • Harmfulness limits: 1 ppm (Benzene), 250 ppm (Acetone), 1000 ppm (Ethanol)
  • Detection limits of sensors: ppb
  • Operating temperatures: room temperature - 100°C
  • Measuring principle: ion mobility spectrometry