80:. With lower operating voltages, the NBTI-induced threshold voltage change is a larger fraction of the logic voltage and disrupts operations. When a clock is gated off, transistors stop switching and NBTI effects accumulate much more rapidly. When the clock is re-enabled, the transistor thresholds have changed and the circuit may not operate. Some low-power designs switch to a low-frequency clock rather than stopping completely in order to mitigate NBTI effects.
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With the introduction of high κ metal gates, a new degradation mechanism has become more important, referred to as PBTI (for positive bias temperature instabilities), which affects nMOS transistor when positively biased. In this case, no interface states are generated and 100% of the Vth degradation
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in the semiconductor are supposed to. When the gate voltage is removed, the trapped charges dissipate over a time scale of milliseconds to hours. The problem has become more acute as transistors have shrunk, as there is less averaging of the effect over a large gate area. Thus, different
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interface traps are generated, and these interface states become positively charged when the pMOS device is biased in the "on" state, i.e. with negative gate voltage. Some interface states may become deactivated when the stress is removed, so that the Vth degradation can be recovered over
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devices (pMOS), since they almost always operate with negative gate-to-source voltage; however, the very same mechanism also affects nMOS transistors when biased in the accumulation regime, i.e. with a negative bias applied to the gate.
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preexisting traps located in the bulk of the dielectric are filled with holes coming from the channel of pMOS. Those traps can be emptied when the stress voltage is removed, so that the Vth degradation can be recovered over
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The existence of two coexisting mechanisms has resulted in scientific controversy over the relative importance of each component, and over the mechanism of generation and recovery of interface states.
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More specifically, over time positive charges become trapped at the oxide-semiconductor boundary underneath the gate of a MOSFET. These positive charges partially cancel the negative gate voltage
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transistors experience different amounts of NBTI, defeating standard circuit design techniques for tolerating manufacturing variability which depend on the close matching of adjacent transistors.
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metal gate stacks are used as an alternative to improve the gate current density for a given equivalent oxide thickness (EOT). Even with the introduction of new materials like
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NBTI has become significant for portable electronics because it interacts badly with two common power-saving techniques: reduced operating voltages and
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penetration. It is known that incorporating nitrogen enhances NBTI. For new technologies (45 nm and shorter nominal channel lengths),
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The details of the mechanisms of NBTI have been debated, but two effects are believed to contribute: trapping of positively charged
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The paradigm shift in understanding the bias temperature instability: From reaction–diffusion to switching oxide traps
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oxide in the gate stack, NBTI remains and is often exacerbated by additional charge trapping in the high-κ layer.
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212:"Negative Bias Temperature Instability (NBTI): Physics, Materials, Process, and Circuit Issues"
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229:”, Microelectronics Reliability, vol 46, no. 2, pp. 278–286, Feb. 2006.
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245:”, Microelectronics Reliability, vol. 45, no. 1, pp. 71–81, Jan. 2005.
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The negative bias temperature instability in MOS devices: A review
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Negative bias temperature instability: What do we understand?
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Controversial issues in negative bias temperature instability
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dependence on time. It is of immediate concern in p-channel
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of a MOSFET. The degradation is often approximated by a
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to reduce the gate leakage current density and prevent
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158:J.H. Stathis, S. Mahapatra, and T. Grasser, “
48:and consequent decrease in drain current and
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44:. NBTI manifests as an increase in the
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30:Negative-bias temperature instability
18:Negative bias temperature instability
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210:Schroder, Dieter K. (August 2005).
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112:is incorporated into the silicon
271:Semiconductor device fabrication
36:) is a key reliability issue in
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235:10.1016/j.microrel.2005.08.001
205:10.1016/j.microrel.2006.10.006
170:10.1016/j.microrel.2017.12.035
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266:Semiconductor device defects
239:M. Alam and S. Mahapatra, “
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108:In sub-micrometer devices
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276:Electronic engineering
142:Hot carrier injection
174:T. Grasser et al., “
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46:threshold voltage
16:(Redirected from
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153:References
114:gate oxide
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136:See also
110:nitrogen
223:S Zafar
187:Bibcode
126:hafnium
84:Physics
66:without
38:MOSFETs
122:high-κ
215:(PDF)
118:boron
101:time.
97:time.
90:holes
34:NBTI
247:doi
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166:doi
58:MOS
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