This document discusses resonant tunneling diodes (RTDs). It begins by motivating the need for signal sources at very high frequencies beyond what conventional transistors can provide. It then introduces normal tunneling diodes and their limitations. RTDs are described as using quantum wells and barriers to allow tunneling only when electrons have a certain minimum energy. This produces negative differential resistance which can be used for oscillation. While RTDs are very fast devices, their output current and power is limited compared to other technologies. More research is needed to improve their power and integration.

1. DEPARTMENT OF ELECTRONICS & COMMUNICATION
ENGINEERING
PONDICHERRY UNIVERSITY
Resonant Tunneling Diodes
PRESENTED BY
SANJEEV K

2. Outline
 Motivation
 Introduction to normal tunneling diode
 Resonant tunneling diode
 Advantages and Limitations
 Conclusion

3. 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.

4. Tunneling diodes (TD)
 P-N diode with heavy
doping (1020 cm3) 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

5. Tunneling diodes (cont.)
 Apply increasing forward bais voltage
 Starting at zero bias:

6. 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.

7. Tunneling diodes (cont.)
 As you increase the basic voltage, a
maximum current will be produced when all
electrons are aligned with the holes

8. Tunneling diodes (cont.)
 As bias voltages continues to increase,
current will decrease because less electrons
are aligned with the holes

9. 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

10. Tunneling diodes (cont.)
 Reverse bias voltage - breakdown
 High leakage current, not a good rectifier

11. .
.
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

12. 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 wellI
barrier
 Increase emitter doping level
 However, PVR will be decreased and
leakage will increaseTo obtain maximum
output power from RTD, high current
density is required

13. 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.

14. 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