Origins and Characteristics of the Threshold Voltage Variability of Quasiballistic Single-Walled Carbon Nanotube Field-Effect Transistors

Abstract

Ultrascaled transistors based on single-walled carbon nanotubes are identified as one of the top candidates for future microprocessor chips as they provide significantly better device performance and scaling properties than conventional silicon technologies. From the perspective of the chip performance, the device variability is as important as the device performance for practical applications. This paper presents a systematic investigation on the origins and characteristics of the threshold voltage (VT) variability of scaled quasiballistic nanotube transistors. Analysis of experimental results from variable-temperature measurement as well as gate oxide thickness scaling studies shows that the random variation from fixed charges present on the oxide surface close to nanotubes dominates the VT variability of nanotube transistors. The VT variability of single-tube transistors has a figure of merit that is quantitatively comparable with that of current silicon devices; and it could be reduced with the adoption of improved device passivation schemes, which might be necessary for practical devices incorporating multiple nanotubes, whose area normalized VT variability becomes worse due to the synergic effects from the limited surface coverage of nanotubes and the nonlinearity of the device off-state leakage current, as predicted by the Monte Carlo simulation.

Variability and reliability analysis in self-assembled multichannel carbon nanotube field-effect transistors

“…3(b) and 3(c), the slope of the simulated results agrees well with the experiment data. But it slightly deviates from the n scaling rule for l(I on ) and 1= ffiffi ffi n p scaling rule 8 for r(I on )/l(I on ) which are based on the assumption of the ideal connection yield (100%). This discrepancy can be attributed to the imperfect connection yield (85%) seen in the experimental data as well as used in the simulation.…”

“…4 While serious integration challenges remain, recent successes with gate-all-around geometries and sub-10 nm channel lengths are extremely encouraging. [5][6][7] Although the progress is impressive, the remaining technological barriers and process variation, including difficulty in assembling CNTs with a controlled pitch, imperfect semiconducting purity, on-state current (I on ) variation, threshold voltage (V t ) variation, 8 and contact resistance, 9 still limit the performance. For practical applications in integrated circuits, each transistor must contain multiple CNTs in parallel in order to drive enough on-state current for high-speed switching as illustrated in Fig.…”

“…8 We propose a statistical model given by Eq. (3) to describe the distribution of V t of multichannel CNTFETs, by simply assuming that V t for a p-type (n-type) multichannel CNTFET is determined by the CNT channel with the most positive (negative) V t (Ref.…”

Endeavor of Iontronics: From Fundamentals to Applications of Ion‐Controlled Electronics

“…The use of electrolyte gating enables the application challenges for nanotube devices to be tackled, which are related to the demand for transistors with an ultrathin‐body and gating all around . There are two ways to utilize carbon nanotubes for transistors: these are: i) to use a single‐strand carbon nanotube as a building block for nanotransistors; and ii) to use thin films of carbon‐nanotube networks as the conducting channels of the transistors . In both situations, electrolyte gating provides much stronger coupling than conventional solid‐state gates.…”

Exploring the Performance Limit of Carbon Nanotube Network Film Field‐Effect Transistors for Digital Integrated Circuit Applications

“…The most remarkable feature in Figure c is that network CNT TFTs are unlikely to simultaneously achieve high g m and low SS, i.e., there is a tradeoff phenomenon between g m and SS, and this tradeoff phenomenon is not observed in conventional FETs or FETs based on individual CNTs . The tradeoff in TFTs actually comes from the asynchronized switching (or different V th ) of individual CNT channels owing to fluctuations in diameter, orientation, and dopant distribution . Since a network TFT channel consists of multiple individual CNTs, the electrical properties of the TFT are the sum of the behaviors of all individual CNTs in the channel.…”