A CMOS smart temperature and humidity sensor with combined readout.

Area of Science:

• Electrical Engineering
• Materials Science
• Sensor Technology

Background:

• Implanted integrated circuits require monitoring of environmental conditions for safe operation.
• Hermeticity of micro-packages is crucial for the reliability of implanted devices.
• Existing monitoring solutions may lack full integration or require external components.

Purpose of the Study:

• To develop a fully-integrated complementary metal-oxide semiconductor (CMOS) sensor for simultaneous temperature and humidity measurements.
• To enable on-chip monitoring of micro-package hermeticity and operating conditions for implanted integrated circuits.
• To ensure the safe and reliable operation of implanted microelectronic devices.

Main Methods:

• A smart sensor utilizing two modes of operation for temperature and humidity conversion into digital frequency ratios.
• Oscillators with timing capacitances and bias currents designed to determine the frequency ratio.
• A reference oscillator with a temperature-dependent current complementary to proportional to absolute temperature (PTAT) current.
• Fabrication of humidity sensors (capacitors) in a commercial 0.18 μm CMOS process with varying areas (0.2 mm² and 1.2 mm²).

Main Results:

• The temperature sensor achieves a normalized sensitivity of approximately 0.77%/°C, with a trade-off in linearity.
• The humidity sensor exhibits a linear response to relative humidity (RH) with a normalized sensitivity of 0.055%/% RH.
• On-chip readout electronics operate from a 5 V supply, consuming approximately 85 µA.

Conclusions:

• The developed integrated CMOS sensor effectively measures both temperature and humidity.
• The sensor is suitable for monitoring micro-package hermeticity and ensuring the operational safety of implanted integrated circuits.
• The device offers a compact, low-power solution for critical environmental monitoring in microelectronic applications.