CMOS Terahertz Sensors and Circuits for Imaging Applications

A low-cost THz sensor, with a broadband high responsivity, low noise equivalent power, and capable of working at room temperature is still a challenge. Moreover, sensor integration with signal processing electronics is required in order to realize compact systems to be used in commercial imaging applications. In this thesis, CMOS FET-based THz detectors and with integrated noise-efficient readout circuits are presented as a solution. In an attempt to improve the THz focal plane arrays state of the art, the use of an imager architecture is proposed, where each sensing element of an array can be addressed individually. This architecture provides better system performance in terms of sensitivity, resolution or speed. A first chip was fabricated in the LFoundry 0.15-µm standard CMOS technology containing a 16 x 16 staring imaging array for terahertz detection in the range of 0.8 THz to 1.5 THz. Each pixel is composed of an antenna, a FET detector, and its readout electronics (a current integrator) so as the whole matrix can be integrated simultaneously. The current integrator employs an amplifier with two offset compensation techniques (chopper and current injection) and an output saturation control by adding and subtracting voltages. A second chip composed of 15 test structures was fabricated in the STMicrolectronics 0.13 µm standard CMOS technology for terahertz detection at 600 GHz, 850 GHz and 1.5 THz. This chip contains different FET detectors (transistor and antenna) and switched-capacitor readout circuits that provide both signal amplification and filtering, improving the system SNR after each operation cycle. A comparative study of their performance is done as a first step towards a future array implementation (THz camera). For both chips, electrical and terahertz characterization results of the designed structures are presented and discussed.