EE PhD Oral Examination - Yeul Na, Sept. 28, 9:30AM, CISX-Aud.

Yeul Na narii at stanford.edu
Wed Sep 28 09:34:00 PDT 2011


Advisor: Krishna Saraswat
Date: Thursday, September 29, 2011
Time: 9:30 AM
Location: Paul Allen Auditorium (Formerly CISX-101)
Title: Novel Phototransistors for Optical Interconnect*
*
Abstract:
Interconnect is one of the major problems in high performance silicon chips
in terms of latency, power and bandwidth. Optical interconnect has potential
benefits to solve such problems. Because of very high carrier frequency,
optical interconnect avoids the resistive loss physics of metal wires, thus
high bandwidth is achievable. However, energy/bit is still high compared to
conventional copper wire in short on-chip/off-chip interconnects. While
lasers and optical modulators promise power requirement for on-chip optical
interconnect lower than copper wire, receivers still consumes high power. To
decrease receiver-end power consumption, receiver-less scheme had been
proposed. To realize this, a device complimentary to photodetector is
needed.

First part of this talk presents the first complimentary device to
photodetector operates at 850nm laser with output current reduction with
incident light. Experiment result successfully showed voltage shift of Id-Vg
curve, which is signature of phototransistor operation, as big as 0.7V. It
also presents the first wavelength tunable complimentary to photodetector
operates at optical communication wavelength range. These phototransistors
have potential to replace current optical receiver circuit and reduce power
dissipation to meet power requirement.

Second part of this talk presents photodetector utilizes phototransistor
concept. Responsivity higher than 700A/W is experimentally shown with 150nW
of incident light in 850nm wavelength, which is higher than external quantum
efficiency of 1000. In addition, small output capacitance of ~2fF/µm and
high scalability are verified from simulation. With these characteristic,
this phototransistor can replace conventional photodiode, and further
decrease power dissipation of optical interconnect.
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