Figure 1
From: Miniaturized thermal acoustic gas sensor based on a CMOS microhotplate and MEMS microphone
Device fabrication. (a) Structure of the CMOS microheater chip (not to scale) which employs a tungsten (W) heating element embedded in a \(\sim\) 4.6 \(\upmu\)m thick silicon dioxide (SiO\(_2\)) membrane formed by deep reactive ion etching. A thermal diode is embedded in the centre of the heated membrane for temperature monitoring. (b) Optical image of the CMOS microheater chip, showing the multi-ring W heating elements and metal heatspreading plates embedded within a SiO\(_2\) membrane. Chip size = 1.08 mm \(\times\) 1.08 mm. (c) Temperature-power characteristics of the microheater up to 450 \(^{\circ }\)C at 60 mW. Inset: hotplate structure. (d) Schematic diagram showing the sensor’s construction. The microheater chip is mounted above the port of a MEMS microphone (TDK model ICS-40300) with a thermal acoustic cavity formed by the etched Si substrate. (e) Optical image of the fabricated thermal acoustic sensor, showing the microheater chip mounted on the MEMS microphone using die bonding film. The opening between the bonding films, to allow gas to diffuse into the thermal acoustic cavity, is visible (dark area).
