MEMS chemoresistive / calorimetric sensors for CO₂ and CH₄

Package case of sensor for individual gas detection

Characteristics

• The MEMS sensors foe CO2(carbon dioxide) and CH4 (methan) have the operating principle based on the change in conductivity due to chemisorbtion a/o calorimetric effects of gas molecules to be detected at the sensitive layer surface.
• The integrated heating element consists of a polysilicon layer underneath the active area. A temperature sensitive resistor will enable precisely temperature control. The sensor is integrated as MEMS in CMOS technology compatible by adding special micromachining processes.
• Different polymeric films sensitivity gases to be analyzed ,exhibit changes of conductance in presence of small gases concentration at ppm level.
• The sensitivity and stability of MEMS sensors are corresponding for applications during the measurement at room temperature of polluted air .or air noxes detection.
• In some cases a temperature of up to 300° could be applied for cleaning the sensitive polymer in order to reuse the sensor
• The product design by using CONVENTOR with the microprocessing technologies summarized specifically for each type as below:

Calorimetric sensor for combustible gas detection CH4 has working between 300-500°C consists of:

• Integrated heater (patterned layer) on the ceramic Si3N4 membrane suspended on four bridges;
• Dielectric (SiO2 or ceramic) deposited hot plate/electric isolation between heater and sensing electrode.
• Al²O³ sol gel deposited
• Temperature platinum sensor, interdigitated electrode
• Chemoresistive sensor for CO2:
• Integrated heater (patterned layer), SiO2 dielectric
• Sensing electrode interdigitated capacitor Ti/Pt or Ti/W/Au
• Gas sensitive layer SnO2, when heated react with gas molecule changes the resistance of interdigitated capacitor
• The resulting heat is detected as an imbalance of the bridge in which the sensor is connected

Packaging case for MEMS sensors integrated chips

Advantages

• Increased reproductibility
• High MEMS sensors miniaturization degree
• Microsystem integration in package (sensors, electrodes)
• Low power consumtion, portable devices approaches
• High working versatility as integrated or individual packaged sensors
• Very low weight ~3g

Gas sensor layout

Applications

• Environment protection and monitoring
• Medical and health care applications
• Industrial facilities and utilities networks and production plants
• Chemical and biochemical technological processing
• Safety and defence industry and applications
• Residential and household appliances

Technical features

Electric characteristics at +25ºC

BONDPADS IDENTIFICATION, CODES AND ASSIGNEMENT

Measurement dates

Exemple of measurement dates for sensor sensitivity working as micropelistor for methan detection

Outlet sensitivity control diagramme