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Since the fabrication of MOSFET, the minimum channel length has been shrinking continuously. The motivation behind this decrease has been an increasing interest in high speed devices and in very large scale integrated circuits. The sustained scaling of conventional bulk device requires innovations to circumvent the barriers of fundamental physics constraining the conventional MOSFET device structure. The limits most often cited are control of the density and location of dopants providing high I on /I off ratio and finite subthreshold slope and quantum-mechanical tunneling of carriers through thin gate from drain to source and from drain to body. The channel depletion width must scale with the channel length to contain the off-state leakage I off. This leads to high doping concentration, which degrade the carrier mobility and causes junction edge leakage due to tunneling. Furthermore, the dopant profile control, in terms of depth and steepness, becomes much more difficult. The gate oxide thickness tox must also scale with the channel length to maintain gate control, proper threshold voltage VT and performance. The thinning of the gate dielectric results in gate tunneling leakage, degrading the circuit performance, power and noise margin.
Now as the gate channel is still reduced the effects which are not dominant while the channel is long come into picture and these affect the device functionality . These are known as the short channel effects. There are various short channel effects which are present as the channel is shrinking down. In electronics, a short-channel effect is an effect whereby a MOSFET in which the channel length is the same order of magnitude as the depletion-layer widths (xdD, xdS) of the source and drain junction, behaves differently from other MOSFETs as the channel length L is reduced to increase both the operation speed and the number of components per chip, the so-called short-channel effects arise.
The short-channel effects are attributed to two physical phenomena:
In particular five different short-channel effects can be distinguished:
Since the fabrication of MOSFET, the minimum channel length has been shrinking continuously. The motivation behind this decrease has been an increasing interest in high speed devices and in very large scale integrated circuits. The sustained scaling of conventional bulk device requires innovations to circumvent the barriers of fundamental physics constraining the conventional MOSFET device structure. The limits most often cited are control of the density and location of dopants providing high I on /I off ratio and finite subthreshold slope and quantum-mechanical tunneling of carriers through thin gate from drain to source and from drain to body. The channel depletion width must scale with the channel length to contain the off-state leakage I off. This leads to high doping concentration, which degrade the carrier mobility and causes junction edge leakage due to tunneling. Furthermore, the dopant profile control, in terms of depth and steepness, becomes much more difficult. The gate oxide thickness tox must also scale with the channel length to maintain gate control, proper threshold voltage VT and performance. The thinning of the gate dielectric results in gate tunneling leakage, degrading the circuit performance, power and noise margin.
Now as the gate channel is still reduced the effects which are not dominant while the channel is long come into picture and these affect the device functionality . These are known as the short channel effects. There are various short channel effects which are present as the channel is shrinking down. In electronics, a short-channel effect is an effect whereby a MOSFET in which the channel length is the same order of magnitude as the depletion-layer widths (xdD, xdS) of the source and drain junction, behaves differently from other MOSFETs as the channel length L is reduced to increase both the operation speed and the number of components per chip, the so-called short-channel effects arise.
The short-channel effects are attributed to two physical phenomena:
- The limitation imposed on electron drift characteristics in the channel,
- The modification of the threshold voltage due to the shortening channel length.
In particular five different short-channel effects can be distinguished:
- drain-induced barrier lowering and punch through
- surface scattering
- velocity saturation
- impact ionization
- hot electron effect
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