Zeshan Ahmad

9.74-THz electronic Far-Infrared detection using Schottky barrier diodes in CMOS

9.74-THz fundamental electronic detection of Far-Infrared (FIR) radiation is demonstrated. The detection along with that at 4.92THz was realized using Schottky-barrier diode detection structures formed without any process modifications in CMOS. Peak optical responsivity (Rv) of 383 and ~14V/W at 4.92 and 9.74THz have been measured. The Rv at 9.74THz is 14X of that for the previously reported highest frequency electronic detection. The shot noise limited NEP at 4.92 and 9.74THz is ~0.43 and ~2nW/√Hz, respectively.

0.39–0.45THz symmetric MOS-varactor frequency tripler in 65-nm CMOS

A broadband passive frequency tripler using an accumulation-mode symmetric MOS varactor (SVAR) in 65-nm bulk CMOS process is demonstrated. The measured output power (Pout) is >-15dBm over a 57GHz band. This tripler incorporating an on-chip patch antenna operates at frequencies between 390 and 456GHz, and achieves a peak Effective Isotropically Radiated Power (EIRP) of -5dBm. The measurement setup limited peak Pout and conversion loss is -3.2dBm and 15.2dB, respectively at 447GHz after antenna gain de-embedding. This is the highest reported output power for all CMOS sources operating above 350GHz and can be integrated with an on-chip input driver amplifier.

20.5 1.4THz, −13dBm-EIRP frequency multiplier chain using symmetric- and asymmetric-CV varactors in 65nm CMOS

THz region of electromagnetic spectrum has unique features making it attractive in spectroscopic studies, material inspection, tera-bit/sec communication, and biological- and non-biological-imaging applications. Owing to challenges in producing sufficiently strong signals, this region of spectrum has been exclusively served by III-V electronics or bulky cryogenic-temperature technologies such as QCLs [1]. Recently, advanced half-THz SiGe technologies and multi-element spatial power-combining techniques to increase the output power were successfully used to generate 0dBm of power at 0.53THz and -17dBm peak EIRP at 0.82THz [2-4]. Both solutions, however, suffer from low realized bandwidths (3%), limiting their utility in a slew of imaging and communication applications. Alternatively, high-quality accumulation-mode symmetric MOS varactors (SVARs) [5] in standard CMOS have been demonstrated as efficient odd-harmonic generators in broadband tripler and quintupler operating around 0.4THz [6] and 0.7THz [7], respectively. In this work, a 1.4THz multiplier chain of 10th order using MOS VARs in a 65nm standard CMOS process is demonstrated. The multiplier incorporates a new asymmetric VAR (ASVAR) for multiplication by 2 in addition to an SVAR for frequency quintupling. The circuit produces -13dBm peak EIRP at 1.33THz and operates over a setup-limited bandwidth of more than 11%. The fully integrated multiplier chain does not require any silicon lens or substrate thinning making it a compact and affordable solution for emerging THz applications.

225–280 GHz receiver for rotational spectroscopy

A fully integrated CMOS receiver for mm-wave rotational spectroscopy is demonstrated. The receiver consists of a sub-harmonic mixer based receiving front-end which down-converts 225-280 GHz RF input to 20 GHz intermediate frequency, a 20-GHz AM demodulator followed by a baseband buffer amplifier, and an 122-139 GHz local oscillator chain which is comprised of a frequency quadrupler and a driver amplifier. The receiver exhibits responsivity of 400-1200 kV/W and noise equivalent power of 0.4 to 1.2 pW/√Hz from 225 to 280 GHz. Detection of ethanol, propionitrile (EtCN), acetonitrile (CH3CN) and acetone in a mixture is demonstrated using the receiver in a rotational spectrometer setup. This is the first demonstration that a CMOS receiver can be used for rotational spectroscopy and that a CMOS circuit can support an existing application at frequencies above 200 GHz.

THz Detection Using p + /n-Well Diodes Fabricated in 45-nm CMOS

Electronic-detection up to ~0.9 THz using p±/n-well junction diodes in a 45-nm bulk CMOS process is demonstrated. Because the 1/f noise corner frequency is ~1 kHz instead of ~10 MHz common to Schottky and diode-connected nMOS transistor detectors, despite lower responsivity, detectors using a p+/n-well diode with an optimized transit time achieve competitive noise equivalent power (NEP) while exhibiting smaller variations. The junction diode has a measured zero-bias cutoff frequency ( fT) of ~1.8 THz. The direct-antenna matched structure can reach a peak optical responsivity (Rv) of 558 V/W at 0.781 THz with a minimum optical NEP of 56 pW/Hz0.5 at a modulation frequency of 100 kHz.

0.65–0.73THz quintupler with an on-chip antenna in 65-nm CMOS

A passive frequency quintupler using a symmetric accumulation MOS varactor is demonstrated for the first time in CMOS. The broadband (0.65-0.73THz) quintupler with an on-chip antenna fabricated in a 65-nm bulk CMOS process reaches a setup limited peak Effective Isotropic Radiated Power (EIRP) of -22dBm at 726GHz, and a minimum conversion loss of 34dB. This highest order multiplier realized in CMOS has the highest EIRP among any lens-less silicon based signal generation circuit operating above 500GHz.

Devices and circuits in CMOS for THz applications

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.

410-GHz CMOS imager using a 4 th sub-harmonic mixer with effective NEP of 0.3 fW/Hz 0.5 at 1-kHz noise bandwidth

A 410-GHz imager consisting of a 4th sub-harmonic mixer formed with an anti-parallel diode-connected NMOS transistor pair, and an on-chip antenna with 4.4-dB simulated gain is demonstrated in 65-nm CMOS. At -1.6-dBm power delivered to the LO input bond pad, the imager achieves 16.8-dB voltage conversion loss and 34.1-dB DSB noise figure. When the noise bandwidth is 1 kHz, sensitivity is -110 dBm, which is 30 dB better than the previously reported CMOS imagers operating near or above 300 GHz. The corresponding effective noise equivalent power is 0.3 fW/Hz0.5.

CMOS sources and detectors for sub-millimeter wave applications

An integrated chain composed of an 195-GHz oscillator with frequency doubled output at ~390 GHz followed by two cascaded ÷2 injection locked frequency dividers with output frequency of ~49 GHz is demonstrated in 45-nm CMOS. The peak power radiated at ~390 GHz by an on-chip antenna is ~2 μW. This work indicates it is possible to phase-lock submillimeter wave signals in CMOS. Polysilicon Gate separated Schottky diodes that can be fabricated without any process modifications in a foundry 130-nm CMOS process are 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/Hz1/2 and responsivity of 5.1kV/W (323V/W without the amplifier). The 860-GHz detector without an amplifier achieves responsivity of 273V/W and NEP of 42pW/Hz1/2.

0.84-THz imaging pixel with a lock-in amplifier in CMOS

An 840-GHz Schottky diode detector is integrated with an analog lock-in amplifier in 130-nm bulk CMOS. The integrated lock-in amplifier can support a modulation frequency of up to 10 MHz with a gain of 54 dB, a dynamic range of 42 dB, and an input referred noise of less than 10 nV/√(Hz) at modulation frequencies higher than 100 kHz. The integrated lock-in amplifier occupies an area of 0.17 mm2 and consumes 4.9 mA from a 1.2-V supply. The detector and on-chip lock-in amplifier combination was used to form terahertz images.