Nansheng Shen

Demonstration of Tunneling FETs Based on Highly Scalable Vertical Silicon Nanowires

This letter demonstrates a vertical silicon-nanowire (SiNW)-based tunneling field-effect transistor (TFET) using CMOS-compatible technology. With a Si p⁺-i- n⁺ tunneling junction, the TFET with a gate length of ~ 200 nm exhibits good subthreshold swing of ~ 70 mV/dec, superior drain-induced-barrier-lowering of ~ 17 mV/V, and excellent <i>I</i> _on - <i>I</i> _off ratio of ~ 10⁷ with a low <i>I</i> _off ( ~ 7&nbsp;pA/mum). The obtained 53 muA/mum <i>I</i> _on can be further enhanced with heterostructures at the tunneling interface. The vertical SiNW-based TFET is proposed to be an excellent candidate for ultralow power and high-density applications.

Multibit Programmable Flash Memory Realized on Vertical Si Nanowire Channel

In this letter, we demonstrate a multibit programmable vertical silicon nanowire (SiNW) SONOS memory using a top-down method. The flash devices realized on highly scaled squarish SiNW down to 20 nm in diagonal show much improved program/erase speed and window along with good retention and endurance characteristics as compared to the ones with a large dimension. The performance improvements with scaling of wire dimensions are attributed to the enhancement of the electric field in tunnel oxide and reduction in blocking oxide as a result of reduced radius of curvatures, particularly on the corners of the squarish wire.

Highly compact 1T-1R architecture (4F 2 footprint) involving fully CMOS compatible vertical GAA nano-pillar transistors and oxide-based RRAM cells exhibiting excellent NVM properties and ultra-low power operation

For the first time, nano-meter-scaled 1T-1R non-volatile memory (NVM) architecture comprising of RRAM cells built on vertical GAA nano-pillar transistors, either junction-less or junction-based, is systematically investigated. Transistors are fabricated using fully CMOS compatible technology and RRAM cells are stacked onto the tip of the nano-pillars (with a diameter down to ~37nm) to achieve a compact 4F2 footprint. In addition, through this platform, different RRAM stacks comprising CMOS friendly materials are studied, and it is found that TiN/Ni/HfO2/n+-Si RRAM cells show excellent switching properties in either bipolar or unipolar mode, including (1) ultra-low switching current/power: SET ~20nA/85nW and RESET ~200pA/700pW, (2) multi-level switchability, (3) good endurance, >105, (4) satisfactory retention, 10 years at 85oC; and (5) fast switching speed ~50ns. Moreover, this vertical (gate-all-around) GAA nano-pillar based 1T-1R architecture provides a more direct and flexible test vehicle to verify the scalability and functionality of RRAM candidates with a dimension close to actual application.

Vertical Silicon Nanowire Platform for Low Power Electronics and Clean Energy Applications

This paper reviews the progress of the vertical top-down nanowire technology platform developed to explore novel device architectures and integration schemes for green electronics and clean energy applications. Under electronics domain, besides having ultimate scaling potential, the vertical wire offers (1) CMOS circuits with much smaller foot print as compared to planar transistor at the same technology node, (2) a natural platform for tunneling FETs, and (3) a route to fabricate stacked nonvolatile memory cells. Under clean energy harvesting area, vertical wires could provide (1) cost reduction in photovoltaic energy conversion through enhanced light trapping and (2) a fully CMOS compatible thermoelectric engine converting waste-heat into electricity. In addition to progress review, we discuss the challenges and future prospects with vertical nanowires platform.

Realizing and and or Functions With Single Vertical-Slit Field-Effect Transistor

This letter experimentally demonstrates and and or functionalities with a single MOS transistor. Device architecture and fabrication follow the recent work on fabrication-based feasibility assessment of junctionless vertical-slit field-effect transistor. Slit width variation is used to realize a particular functionality-wider for or function and narrower for and function. The fabricated n-type devices with the and and or functionalities exhibit good electrical performance: low off current (<; 5 pA/μm) and high ION/IOFF ratio (>; 106). Furthermore, we briefly discuss the implication of these devices in CMOS NAND logic implementation.

Vertically Stacked and Independently Controlled Twin-Gate MOSFETs on a Single Si Nanowire

For the first time, we demonstrate the fabrication of two independently controlled gate-all-around MOSFETs on a single vertical silicon nanowire using CMOS process technology. The second gate is vertically stacked on top of the first gate without occupying additional area and thereby achieving true 3-D integration. The fabricated devices exhibit very low leakage, tunability in drain current, as well as “AND” gate functionality with 50% reduction in area for both n- and p-type MOSFETs. The twin-gate device structure is also promising for implementing other device types such as stacked SONOS memory and tunneling FET. We anticipate that our vertically integrated device architecture will provide unique opportunities for realizing ultra-dense CMOS logic on a single nanowire.

High-Performance Poly-Si Vertical Nanowire Thin-Film Transistor and the Inverter Demonstration

In this letter, gate-all-around vertical nanowire (NW) polycrystalline silicon (poly-Si) thin-film transistors (TFTs) are demonstrated using a CMOS-compatible process. Both Nand P-TFT devices (with gate length down to 100 nm and a wire diameter of ~30 nm) exhibit good transistor performance, e.g., high Ion/Ioff ratio of >; 106, low subthreshold slope (SS ~ 100 mV/dec), and reasonable drain-induced barrier lowering [(DIBL); ~50 mV/V] with a wire diameter of ~30 nm. Inverters have been successfully fabricated based on the poly-Si NW TFTs, exhibiting well-behaved transfer characteristics.