resonant tunnelling devices a survey on their progress
TRANSCRIPT
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Resonant Tunnelling Devices
A survey on their progress
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CMOS Scaling has been key to performance increase
CMOS scaling gives us three things: Higher clock More components Same cost
We are currently at 90nm 65nm in 2006 Everybody’s favourite line: Moore’s law will hit a wall
(so far all false) Some technology will eventually replace CMOS What is that technology?
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Research idea: Find the next CMOS
So many post-CMSO proposals Quantum computing Molecular electronics DNA computing … (countless)
Hear about “breakthroughs” everyday Yet we’re still using silicon transistors So are we really?
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How things fit
Plain CMOS scaling will carry us to 10nm (and maybe more)
That means at least another 10-15 years before we must switch to a new tech
But it might make sense to switch ealier Key theme: below 100nm, two options are
available: Smaller CMOS Quantum-effect based devices
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What about all the “breakthroughs”?
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Why Resonant Tunnelling Devices?
Works at room temperature! Extremely high switching speed (THz) Low power consumption Well demonstrated uses
Logic gates, fast adders, ADC etc. Can be integrated on existing processes In one word: Feasible
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What we’ve been using: The MOSFET
Source: Scientific American
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Resonant Tunnelling Diodes
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Resonant Tunnelling Diodes
Fundamentally different operating principle Quantisation Quantum tunnelling
Computation comes from Negative Differential Resistance (NDR)
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Negative Differential Resistance
Need high peak to Valley Current Ratio (PVCR)PVCR of 2-4 desirable
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Example Circuit: TSRAM
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Example Circuit: Shift Register
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Problem
Up until now, all usable circuits made using III-V compound semiconductors Eg. GaAs, InP Good PVCR and current density Good for high frequency switching applications CMOS incompatible
Need a silicon solution before any chance of mass uptake
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Silicon based RTDs
Prior to 1998, Si based RTD displayed no usable NDR
In 1998, Rommel et al produced first Si/SiGe/Si RITD with NDR at room temperature
RITD exhibits better PVCR
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Integration with CMOS
In 2003, monolithic integration with CMOS demonstrated
Performance comparable to discrete RITD
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Integrated FET/RITD
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What does it mean for architecture?
CMOS / RTD hybrid circuits Factor of reduction in component complexity Higher operating frequency Lower power consumption
TSRAM 1 transistor SRAM with DRAM density on chip Greatly reduced power consumption More design options with eDRAM
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A Roadmap to RTDs?
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Take home message
CMOS scaling will continue, one way or another Double Gate MOSFET will get us to 10nm Plenty of new options
The transistor of the future will exploit quantum effects SET, QD, Molecular, Spin transistor
Silicon RTDs can now be integrated with CMOS Excellent for extending CMOS
Good chance they will be the first quantum effect devices to become mainstream