Download Silicon-nanowire Field Effect Transistor (SiNW FET)

Resonant Tunneling
Diodes
Johnny Ling, University of Rochester
December 16th, 2006
Outline
► Motivation
► Introduction
► Resonant
to normal tunneling diode
tunneling diode
► Advantages
► Conclusion
and Limitations
Motivation
► An
increasing number of applications that require
signal sources at very high frequencies (3001500GHz)
► Ultimate limit on the current trend of down-scaling
transistors and integrated circuits to achieve faster
speeds and lower power consumption
► The highest frequency conventional transistor
oscillator built today is only about 215 GHz.
Tunneling diodes (TD)
►
►
►
P-N diode with heavy
doping (1020 cm-3) in both
regions (Degenerately
doped)
The depletion region is
very narrow (<10nm)
High concentration of
electrons in the
conduction band of Ntype and holes in the
valence band of P-type
material
Tunneling Diodes (cont.)
► Apply
increasing forward bias voltage
► Starting
at zero bias:
Tunneling Diodes (cont.)
► Electrons
in N-region conduction band are
energetically aligned to the holes in the valence
band of P-region. Tunneling occurs. Forward
current is produced.
Tunneling Diodes (cont.)
► As
you increase the bias voltage, a
maximum current will be produced when all
electrons are aligned with the holes
Tunneling Diodes (cont.)
► As
bias voltages continues to increase,
current will decrease because less electrons
are aligned with the holes
Tunneling Diodes (cont.)
► As
the bias voltage continues to increase,
electrons are no longer energetically aligned
with the holes and the diffusion current
dominates over tunneling
Tunneling Diodes (cont.)
► Reverse
bias voltage – breakdown
► High leakage current, not a good rectifier
Resonant Tunneling Diode (RTD)
►
►
Electrons must have a certain minimum energy above the
energy level of the quantized states in the quantum well in
order for tunneling to occur. Once the bias voltage is big
enough to provide enough energy, RTDs looks like a normal
TD
In reverse bias, RTDs do not have large leakage current
Negative Differential Resistance(NDR)
►Characterized
by the current peak to valley ratio
(PVR=I/V)
►To achieve maximize dynamic range, high PVR is desired.
►To obtain maximum output power from RTD, high
current density is required
►Decrease the thickness of the quantum well barrier
►Increase emitter doping level
►However, PVR will be decreased and leakage will
increase
Advantages and Limitations
► RTDs
is considered among the fastest devices
because tunneling is very fast and is not transittime limited as in CMOS technology, etc.
► RTDs provide a low leakage current when a
reverse bias is applied.
► Large dynamic range within a small input voltage
range
► However, the output current and power of RTDs is
very limited compared to CMOS.
Conclusion
► RTDs
is much faster than any other conventional
transistor.
► Very important alternative as transistor technology
continues to scale down to the nanometer range
► Very good rectifier – low leakage current
► Much research needs to be done to improve
the output power and also to integrate them with
conventional transistors