Silicon-nanowire Field Effect Transistor (SiNW FET) - University of ...

heartlustElectronics - Devices

Nov 2, 2013 (3 years and 9 months ago)

88 views

Resonant Tunneling
Diodes

Johnny Ling, University of Rochester

December 16
th
, 2006


Outline


Motivation



Introduction to normal tunneling diode



Resonant tunneling diode



Advantages and Limitations



Conclusion


Motivation


An increasing number of applications that require
signal sources at very high frequencies (300
-
1500GHz)


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 (10
20

cm
-
3
) in both
regions (Degenerately
doped)


The depletion region is
very narrow (<10nm)


High concentration of
electrons in the
conduction band of N
-
type 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 transit
-
time 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