Transcript Tunneling Devices
Slide 1
Tunneling Devices
Slide 2
Motivation
• Scaling: some proposed tunneling field
effect transistor (TFET) designs do not
suffer from short channel effects
• Power Dissipation: TFETs can beat the 60
mV/decade sub-threshold swing of
MOSFETs
• Design Flexibility: Circuits can be made
with fewer devices
Slide 3
Obligatory Moore’s Law
human brain in 2012?
Reference
http://www.intel.com/research/silicon/mooreslaw.htm
Slide 4
What’s so great about a
tunneling device?
• Lower sub-threshold swing can allow for
lower operating voltages to be used
• Negative differential resistance (NDR)
properties can be exploited to create
simpler designs for bi-stable circuits,
differential comparators, oscillators, etc.
• Leads to chips that consume less power
Slide 5
Tunneling
• Tunneling is a quantum mechanical
phenomenon with no analog in classical
physics
• Occurs when an electron passes through
a potential barrier without having enough
energy to do so
Slide 6
(Esaki) Tunnel Diode (TD)
• Simplest tunneling device
• Heavily-doped pn junction
EF
– Leads to overlap of conduction and valence
bands
• Carriers are able to tunnel inter-band
• Tunneling goes exponentially with
tunneling distance
– Requires junction to be abrupt
EC
EV
Slide 7
Band-to-Band Tunneling in a
Tunnel Diode (c)
(e)
I
(b)
(d)
V
EC
(a)
EV
EF
(a)
(b)
(c)
(d)
(e)
Slide 8
Figures of Merit
Peak current
100 kA/cm2
Peak-to-Valley Ratio (PVR)
I
V
Slide 9
Bi-stable Configuration
V
I
D1
X
D2
X1
X2 V
Slide 10
TD Differential Comparator
V
CC
D3
X
M3
D4
CK
M4
D1
D2
VOUT
VOUT
VIN
RL
M 1 M2
I1
VIN
RL
I2
ITAIL
-VEE
Slide 11
Direct vs. Indirect Tunneling
Direct
Indirect
Indirect materials require phonons to tunnel, thus
reducing the probability of a tunneling event
Slide 12
Tunnel Current Expressions
m*1/ 2 EG3 / 2
T exp 2 2eF
E
3
Jt
1/ 2
q m*
2
4 2eF
3
Va
4 2 E g
2
2 Et
exp
E
1/ 2
*
m EG
exp(
- 4 2m *E g
3q
3/ 2
)
Tunneling Devices
Slide 2
Motivation
• Scaling: some proposed tunneling field
effect transistor (TFET) designs do not
suffer from short channel effects
• Power Dissipation: TFETs can beat the 60
mV/decade sub-threshold swing of
MOSFETs
• Design Flexibility: Circuits can be made
with fewer devices
Slide 3
Obligatory Moore’s Law
human brain in 2012?
Reference
http://www.intel.com/research/silicon/mooreslaw.htm
Slide 4
What’s so great about a
tunneling device?
• Lower sub-threshold swing can allow for
lower operating voltages to be used
• Negative differential resistance (NDR)
properties can be exploited to create
simpler designs for bi-stable circuits,
differential comparators, oscillators, etc.
• Leads to chips that consume less power
Slide 5
Tunneling
• Tunneling is a quantum mechanical
phenomenon with no analog in classical
physics
• Occurs when an electron passes through
a potential barrier without having enough
energy to do so
Slide 6
(Esaki) Tunnel Diode (TD)
• Simplest tunneling device
• Heavily-doped pn junction
EF
– Leads to overlap of conduction and valence
bands
• Carriers are able to tunnel inter-band
• Tunneling goes exponentially with
tunneling distance
– Requires junction to be abrupt
EC
EV
Slide 7
Band-to-Band Tunneling in a
Tunnel Diode (c)
(e)
I
(b)
(d)
V
EC
(a)
EV
EF
(a)
(b)
(c)
(d)
(e)
Slide 8
Figures of Merit
Peak current
100 kA/cm2
Peak-to-Valley Ratio (PVR)
I
V
Slide 9
Bi-stable Configuration
V
I
D1
X
D2
X1
X2 V
Slide 10
TD Differential Comparator
V
CC
D3
X
M3
D4
CK
M4
D1
D2
VOUT
VOUT
VIN
RL
M 1 M2
I1
VIN
RL
I2
ITAIL
-VEE
Slide 11
Direct vs. Indirect Tunneling
Direct
Indirect
Indirect materials require phonons to tunnel, thus
reducing the probability of a tunneling event
Slide 12
Tunnel Current Expressions
m*1/ 2 EG3 / 2
T exp 2 2eF
E
3
Jt
1/ 2
q m*
2
4 2eF
3
Va
4 2 E g
2
2 Et
exp
E
1/ 2
*
m EG
exp(
- 4 2m *E g
3q
3/ 2
)