Subthreshold swing (SW)

Subthreshold Swing (SW)
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Subthreshold leakage (ISubVth)

S-RCAT (Sphere-shaped-Recess-Channel-Array Transistor) technology is a modified structure of the RCAT (Recess-Channel-Array Transistor) and shows an excellent scalability of recessed-channel structure to sub-50 nm feature size. [1] Comparing to the RCAT structure, the S-RCAT demonstrated superior characteristics in:
          i) DIBL,
          ii) Subthreshold swing (SW),
          iii) Body effect,
          iv) Junction leakage current,
          v) Data retention time.

In general, the preconductive subthreshold regime is on the order of a few hunded millielectronvolts. Figure 2411 shows the intrinsic, subthreshold, and conducting regimes of a FET. The subthreshold regime is characterized by a sharp increase in the log(I_drain) versus V_g plot. The subthreshold swing, S, is defined as the increase in gate voltage per 10-fold increase in source-drain current, in the range of 250 - 450 mV decade^-1. The subthreshold swing, S, can be used to estimate the two-dimensional trap density within the active region of quantum dots at the FET interface. [3] The log scale transfer characteristic includes:
          i) The intrinsic regimes.
          ii) The subthreshold regimes.
          iii) The conducting regimes.

Figure 2411. (a) Linear scale transfer characteristic of an iodide dissolved in methanol ligand-exchanged nanocrystal FET, highlighting the threshold voltage, V_v, as the intersection of the linear conductance region with the voltage axis. (b) Log scale transfer characteristic, highlighting the intrinsic, subthreshold, and conducting regimes. [3]

For a wiggling active area (fin) in an advanced 1x DRAM process, from the logarithmic I_d-V_g curve, it was shown that the fatter fin exhibited much higher off-state leakage and larger subthreshold swing, indicating that channel controllability is weak. The leakage in a fatter fin dramatically increased at higher drain voltages, while it was not so obviously changed in a thinner fin. [2]

In theory, for FinFETs, the OFF-current, leakage current, GIDL, and subthreshold swing increase with increasing temperature, whereas the ON-current, low-field mobility, and threshold voltage decrease with temperature. [4]

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[1] J.Y. Kim, H.J. Oh, D.S. Woo, Y.S. Lee, D.H. Kim, S.E.Kim, G.W. Ha, H.J Kim, N.J. Kang, J.M. Park, Y.S. Hwang, D.I. Kim, B.J. Park, M. Huh, B.H. Lee, S.B. Kim, M.H. Cho, M.Y. Jung, Y.I. Kim, C. Jin, D.W. Shin, M.S. Shim, C.S. Lee*, W.S. Lee*, J.C. Park**, G.Y. Jin, Y.J. Park and Kinam Kim, S-RCAT (Sphere-shaped-Recess-Channel-Array Transistor) Technology for 70nm DRAM feature size and beyond, Digest of Technical Papers. 2005 Symposium on VLSI Technology, DOI: 10.1109/.2005.1469201, 2005.
[2] QingPeng Wang, Yu De Chen, Jacky Huang and Ervin Joseph, A Study of Wiggling AA modeling and Its Impact on the Device Performance in Advanced DRAM, 2020 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD), DOI: 10.23919/SISPAD49475.2020.9241640, 2020.
[3] Philipp Stadler, Brandon R. Sutherland, Yuan Ren, Zhijun Ning, Arash Simchi, Susanna M. Thon, Sjoerd Hoogland, and Edward H. Sargent, Joint Mapping of Mobility and Trap Density in Colloidal Quantum Dot Solids, ACS Nano 2013, 7, 7, 5757–5762.
[4] Amer Diab, Galo A. Torres Sevilla, Sorin Cristoloveanu, and Muhammad Mustafa Hussain, Room to High Temperature Measurements of Flexible SOI FinFETs With Sub-20-nm Fins, IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 61, NO. 12, DECEMBER 2014.

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