Ray Chen

Receiver-less optical clock injection for clock distribution networks

We present a new technique of injecting clocks optically onto CMOS chips without the use of a receiver amplifier. We discuss the benefits of such a direct approach and present proof-of-principle experiments of the technique. We analytically compare a receiver-less optical clock distribution and an electrical clock distribution in a fan-out-of-four clock tree to evaluate the timing and power benefits of the optical approach for present microprocessors. We also compare receiver-less direct injection of optical clocks to trans-impedance receiver based injection within the same distribution framework.

MINVDD testing for weak CMOS ICs

A weak chip is one that contains flaws-defects that do not interfere with correct circuit operation at normal conditions but may cause intermittent or early-life failures. MINVDD testing can detect weak CMOS chips. The minvdd of a chip is the minimum supply voltage value at which a chip can function correctly. It can be used to differentiate between good chips and weak chips. In the first part of this paper, we will study several types of flaws to demonstrate the effectiveness of MINVDD testing. Experimental results show that MINVDD testing is as effective as VLV testing for screening out burn-in rejects. In the second part of this paper, we propose test conditions for low voltage testing, including test voltage, test timing and test sets. Experimental results are presented to validate our proposal.

MSM-based integrated CMOS wavelength-tunable optical receiver

We demonstrate a novel GaAs-metal-semiconductor-metal (MSM)-based wavelength-selective photodetector integrated with its complementary metal-oxide-semiconductor (CMOS) driver and receiver. This receiver has /spl sim/1-ns wavelength switching access time and has been shown to detect 4 bits of 460-Mb/s (2.17-ns bit period) emulated data in nonreturn-to-zero format during the enabled 8.68-ns windows. The demonstrated channel spacing is /spl sim/70.8 GHz. To our knowledge, this is the fastest reported wavelength switching time for a tunable optical receiver.

Novel electrically controlled rapidly wavelength selective photodetection using MSMs

A novel electrically controlled tunable metal-semiconductor-metal (MSM) photodetector is introduced and experimentally demonstrated with 2.5-ns wavelength-switching access time on a GaAs chip for switching between two wavelengths. This detector has a demonstrated 20.1-dB ON/OFF contrast ratio between the selected and the rejected wavelength and can resolve 179-GHz spaced wavelength-division multiplexing channels. In addition, device wavelength switching is achieved with a differential input voltage swing of /spl plusmn/1.65 V. This low bias voltage makes it compatible with complementary metal-oxide semiconductor (CMOS) control electronics for rapid switching.

Novel on-chip fully monolithic integration of GaAs devices with completely fabricated Si CMOS circuits

We monolithically integrated polycrystalline GaAs metal-semiconductor-metal (MSM) photoconductive switches with a completely fabricated Si-CMOS amplifier and obtained a properly functional optical receiver, without altering the Si circuit performance. To our knowledge, this is the first time a fully monolithic on-chip integration has been achieved.

Receiverless clocking of a CMOS digital circuit using short optical pulses

We use short optical pulses to clock a digital logic block without using clock receivers. We measure 12 ps rms jitter at the output of a digital PRBS with optical clocking and 30 ps with electrical clocking.

Novel electrically tunable MSM photodetector for resolving WDM channels

We present a novel MSM (metal-semiconductor-metal) based tunable photodetector for discrimination between two wavelengths with a 365 GHz channel spacing. If integrated with CMOS circuits, this photodetector has the potential to perform high-speed channel switching in WDM-based systems.

Efficient luminescence in highly tensile-strained germanium

Up to 2.3% biaxial tensile-strained Ge layers have been grown on InGaAs/GaAs buffer layers. A dramatic increase in low temperature photoluminescence intensity for >2% strained Ge confirms the existence of a direct band gap Ge.

Receiver-less optical clock distribution using short pulses

We have used short optical pulses to clock digital logic on CMOS, without using clock receivers. We present the benefits of this approach compared to electrical clock distribution by evaluating the resulting timing and power savings in a fan-out-of-four clock tree modeled after modern microprocessors.

Spectral shaping of electrically controlled MSM-based rapidly tunable photodetectors

We spectrally shape the response of a tunable photodetector in the telecommunication C-band by illuminating the device with more than one interference pattern. The experimental results are in excellent agreement with the mathematical models.