High-performance top-gated carbon nanotube field-effect transistors (CNT FETs) with a gate length of 5 nanometers can be fabricated that perform better than silicon complementary metal-oxide semiconductor (CMOS) FETs at the same scale. A scaling trend study revealed that the scaled CNT-based devices, which use graphene contacts, can operate much faster and at much lower supply voltage (0.4 versus 0.7 volts) and with much smaller subthreshold slope (typically 73 millivolts per decade). The 5-nanometer CNT FETs approached the quantum limit of FETs by using only one electron per switching operation. In addition, the contact length of the CNT CMOS devices was also scaled down to 25 nanometers, and a CMOS inverter with a total pitch size of 240 nanometers was also demonstrated.

http://science.sciencemag.org/content/sci/355/6322/271.full.pdf

Scaling carbon nanotube complementary transistors to 5-nm gate lengths

The scaling of transistors to sub-10 nm dimensions is strongly limited by their contact resistance (RC). Here we present a systematic study of scaling MoS2 devices and contacts with varying electrode metals and controlled deposition conditions, over a wide range of temperatures (80 to 500 K), carrier densities (1012 to 1013 cm–2), and contact dimensions (20 to 500 nm). We uncover that Au deposited in ultra-high vacuum (∼10–9 Torr) yields three times lower RC than under normal conditions, reaching 740 Ω·μm and specific contact resistivity 3 × 10–7 Ω·cm2, stable for over four months. Modeling reveals separate RC contributions from the Schottky barrier and the series access resistance, providing key insights on how to further improve scaling of MoS2 contacts and transistor dimensions. The contact transfer length is ∼35 nm at 300 K, which is verified experimentally using devices with 20 nm contacts and 70 nm contact pitch (CP), equivalent to the “14 nm” technology node.

Improved Contacts to MoS2 Transistors by Ultra-High Vacuum Metal Deposition

https://cyberleninka.org/article/n/1380904.pdf

ASAP7: A 7-nm finFET predictive process design kit

A new benchmarking of beyond-CMOS exploratory devices for logic integrated circuits is presented. It includes new devices with ferroelectric, straintronic, and orbitronic computational state variables. Standby power treatment and memory circuits are included. The set of circuits is extended to sequential logic, including arithmetic logic units. The conclusion that tunneling field-effect transistors are the leading low-power option is reinforced. Ferroelectric transistors may present an attractive option with faster switching delay. Magnetoelectric effects are more energy efficient than spin transfer torque, but the switching speed of magnetization is a limitation. This article enables a better focus on promising beyond-CMOS exploratory devices.

Benchmarking of Beyond-CMOS Exploratory Devices for Logic Integrated Circuits

An efficient way to reduce the power consumption of electronic devices is to lower the supply voltage, but this voltage is restricted by the thermionic limit of subthreshold swing (SS), 60 millivolts per decade, in field-effect transistors (FETs). We show that a graphene Dirac source (DS) with a much narrower electron density distribution around the Fermi level than that of conventional FETs can lower SS. A DS-FET with a carbon nanotube channel provided an average SS of 40 millivolts per decade over four decades of current at room temperature and high device current I60 of up to 40 microamperes per micrometer at 60 millivolts per decade. When compared with state-of-the-art silicon 14-nanometer node FETs, a similar on-state current Ion is realized but at a much lower supply voltage of 0.5 volts (versus 0.7 volts for silicon) and a much steeper SS below 35 millivolts per decade in the off-state.

https://science.sciencemag.org/content/sci/361/6400/387.full.pdf

Dirac-source field-effect transistors as energy-efficient, high-performance electronic switches

A 14nm logic technology using 2nd-generation FinFET transistors with a novel subfin doping technique, self-aligned double patterning (SADP) for critical patterning layers, and air-gapped interconnects at performance-critical layers is described. The transistors feature rectangular fins with 8nm fin width and 42nm fin height, 4th generation high-k metal gate, and 6th-generation strained silicon, resulting in the highest drive currents yet reported for 14nm technology. This technology is in high-volume manufacturing.

A 14nm logic technology featuring 2 nd -generation FinFET, air-gapped interconnects, self-aligned double patterning and a 0.0588 µm 2 SRAM cell size

: Increasing power density is a daunting challenge for continued MOSFET scaling due to non-scalability of the thermal voltage kBT/q. To circumvent this CMOS power crisis and to allow for aggressive supply voltage reduction alternative switching device designs have been proposed and demonstrated to achieve steeper than 60mV/dec subthreshold swing (S). This dissertation begins with a general overview of the physics and operation of these MOSFET-replacement devices. It then applies circuit-level metrics to establish evaluation guidelines for assessing the promise of these alternative transistor designs. This dissertation then investigates the abrupt "pull-in" effect of an electrostatically actuated beam to achieve abrupt switching behavior in the nanoelectro-mechanical field effect transistor (NEMFET). To facilitate low-voltage NEMFET design, the Euler-Bernoulli beam equation is solved simultaneously with the Poisson equation in order to accurately model the switching behavior of a NEMFET. The impact of various transistor design parameters on the gate pull-in voltage and release voltage are examined. A unified pull-in/release voltage model is developed. Finally, this dissertation proposes the use of micro-relays for zero-standby-power digital logic applications. To mitigate the contact reliability issue, it is demonstrated that since relatively high on-state resistance can be tolerated while extremely high endurance is a necessity, hard contacting electrode materials and operation with low contact force are preferred for reliable circuit operation. Using this contact design approach, a reliable relay technology that employs titanium dioxide (TiO2) coated tungsten (W) electrodes is developed for digital logic applications.

/pdf/mosfet-replacement-devices-for-energy-efficient-digital-bjj7dmatz1.pdf

Hei Kam

Papers

A 14nm logic technology featuring 2 nd -generation FinFET, air-gapped interconnects, self-aligned double patterning and a 0.0588 µm 2 SRAM cell size

MOSFET Replacement Devices for Energy-Efficient Digital Integrated Circuits