A Single-Chip CMOS Micro-Hotplate Array for Hazardous-Gas Detection and

Material Characterization

Presentation by

Hörður Mar Tómasson

16. October 2006

The principle of operation

• A sample of gas/material is exposed to a temperature sweep.

• The heat absorbtion of the material at the different temperatures is measured.

• The electrical resistance of a gas-sensitive film is measured.

The hotplate

• A heater ring of polysilicon

• Layers of silicon oxide/nitride provide thermal isolation from the chip bulk.

• Polysilicon temperature sensor in the centre

• Heated area diameter: 100 µm

• Electrical resistance of heater: 125 Ω.

• Power efficiency: 10.0°C/mW

Electrodes

• Structure of the electrodes that contact the sensitive layer or the sample:

• CMOS aluminium metallization

• Ti/W layer that blocks diffusion

• Platinum film

Temperature control

• 10 bit ADC for the temperature sensor

• PID controller

• 10 bit DAC

• DC amplifier drives the heater

The circuit

• Temperature control loops

• Chip bulk temperature measurement

• Resistance measurement of material

• Chip communication

• Logic for development of new controllers using an FPGA