Chuying Mao

Progress and Challenges Towards Terahertz CMOS Integrated Circuits

Key components of systems operating at high millimeter wave and sub-millimeter wave/terahertz frequencies, a 140-GHz fundamental mode voltage controlled oscillator (VCO) in 90-nm CMOS, a 410-GHz push-push VCO with an on-chip patch antenna in 45-nm CMOS, and a 125-GHz Schottky diode frequency doubler, a 50-GHz phase-locked loop with a frequency doubled output at 100 GHz, a 180-GHz Schottky diode detector and a 700-GHz plasma wave detector in 130-nm CMOS are demonstrated. Based on these, and the performance trends of nMOS transistors and Schottky diodes fabricated in CMOS, paths to terahertz CMOS circuits and systems including key challenges that must be addressed are suggested. The terahertz CMOS is a new opportunity for the silicon integrated circuits community.

125-GHz Diode Frequency Doubler in 0.13-

The first mm-wave Schottky diode frequency doubler fabricated in CMOS is demonstrated. The doubler built in 130-nm CMOS uses a balanced topology with two shunt Schottky barrier diodes, and exhibits ~ 10-dB conversion loss as well as -1.5-dBm output power at 125 GHz. The input matching is better than -10 dB from 61 to 66 GHz. The rejection of fundamental signal at output is greater than 12 dB for input frequency from 61 to 66 GHz. The doubler can generate signals up to 140 GHz.

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The electromagnetic spectrum between 300GHz and 3THz is broadly referred as terahertz [1]. The utility of this portion of spectrum for detection of chemicals and bio agents, for imaging of concealed weapons, cancer cells and manufacturing defects [1, 2], and for studying chemical species using electron paramagnetic resonance, as well as, in short range radars and secured high data rate communications has been demonstrated. However, high cost and low level of integration for III–V devices needed for the systems have limited their wide use. The improvements in the high frequency capability of CMOS have made it possible to consider CMOS as a lower cost alternative for realizing the systems that can greatly expand the use of this spectrum range.

CMOS

The first mm-wave varistor mode Schottky diode frequency doubler fabricated in CMOS is demonstrated. The doubler exhibits 14 dB conversion loss, -11 dBm output power at 132 GHz and 6 GHz 3-dB output bandwidth from 128 to 134 GHz. The input matching is better than -10 dB and the rejection of fundamental signal at output is greater than 14 dB from 62 to 70 GHz.

Towards terahertz operation of CMOS

The first complementary anti-parallel Schottky diode frequency tripler in CMOS is demonstrated. The tripler exhibits ~34-dB minimum conversion loss, -24-dBm maximum output power at 150 GHz, and 3 db output frequency range of ~10 GHz.

Millimeter Wave Varistor Mode Schottky Diode Frequency Doubler in CMOS

A 140-GHz fundamental mode VCO in 90-nm CMOS and a 410-GHz push-push VCO in 45-nm CMOS, and a 125-GHz Schottky diode frequency doubler, a 50-GHz phase locked loop with a frequency doubled output at 100 GHz, a 180-GHz Schottky diode detector and a 700-GHz plasma wave detector in 130-nm CMOS have been demonstrated. Based on these, paths to terahertz CMOS circuits are suggested.

150 GHz Complementary Anti-Parallel Diode Frequency Tripler in 130 nm CMOS

High volume millimeter wave applications are emerging. With the speed improvement of CMOS, sub-millimeter wave operation of CMOS circuits appears to be possible. in traditional millimeter and sub-millimeter wave systems, discrete Schottky diodes are widely utilized. This paper reviews the high frequency performance of junction and Schottky diodes fabricated in CMOS without any process modification, and circuits using the diodes, as well as suggesting approaches that can improve their performance.

Paths to terahertz CMOS integrated circuits

Recent advances of CMOS technology and circuits have made it an alternative for realizing capable and affordable THz systems. With process and circuit optimization, it should be possible to generate useful power and coherently detect signals at frequencies beyond 1THz, and incoherently detect signals at 40THz in CMOS.

Diodes in CMOS for millimeter and sub-millimeter wave circuits

Using Polysilicon Gate Separated Schottky Diode structures that can be fabricated without any process modifications in a foundry digital 130-nm CMOS process, cut-off frequency of ~2 THz has been measured. In addition, exploiting the complementary of CMOS technology, an anti-parallel diode pair with cut-off frequency of ~660 GHz consisting of an n-type and a p-type Schottky diode has been demonstrated in the same 130-nm CMOS process. Using the diodes, a frequency doubler and a tripler have been demonstrated. Additionally, the diodes have been utilized to implement 280-GHz and 860-GHz detectors for imaging. A fully-integrated 280-GHz 4×4 imager array exhibits measured NEP of 29pW/Hz½ and responsivity of 5.1kV/W (323V/W without the amplifier). The 860-GHz detector without an amplifier achieves responsivity of 355V/W and NEP of 32pW/Hz½. The NEP at 860GHz is 2X better than the best reported performance of MOSFET-based imagers without a silicon lens attached to the chip.

Devices and circuits in CMOS for THz applications

The feasibility of CMOS circuits operating at frequencies in the upper millimeter wave and low sub-millimeter frequency regions has been demonstrated. A 140-GHz fundamental mode VCO in 90-nm CMOS, a 410-GHz push-push VCO in 45-nm CMOS, and a 180-GHz detector circuit in 130-nm CMOS have been demonstrated. With the continued scaling of MOS transistors, 1-THz CMOS circuits will be possible. Though these results are significant, output power of signal generators must be increased and acceptable noise performance of detectors must be achieved in order to demonstrate the applicability of CMOS for implementing practical terahertz systems.