High-speed bipolar phototransistors in a 180 nm CMOS process

Area of Science:

• Optoelectronics
• Semiconductor Devices
• Integrated Circuits

Background:

• Phototransistors are key components in optoelectronic systems.
• Standard CMOS processes offer a pathway for cost-effective integration.
• High-speed photodetectors are crucial for many advanced applications.

Purpose of the Study:

• To present high-speed PNP phototransistors fabricated in a standard 180nm CMOS process.
• To characterize their optical and electrical performance.
• To evaluate their suitability for integrated optoelectronic circuits.

Main Methods:

• Fabrication of PNP phototransistors in 40x40 μm² and 100x100 μm² sizes using a 180nm CMOS process.
• Optical characterization at wavelengths of 410, 675, and 850 nm.
• Evaluation of bandwidth and dynamic responsivity.

Main Results:

• Achieved bandwidths up to 92 MHz.
• Demonstrated dynamic responsivities up to 2.95 A/W.
• Varied phototransistor characteristics based on base and emitter area designs.

Conclusions:

• The developed PNP phototransistors are suitable for high-speed photosensitive optical applications requiring inherent amplification.
• Standard silicon CMOS implementation enables cost-effective integration of optoelectronic circuits.
• Potential applications include low-cost, high-speed image sensors and opto-couplers.