Jente B. Kuang

Interplay Between Process-Induced and Statistical Variability in 14-nm CMOS Technology Double-Gate SOI FinFETs

This paper presents a comprehensive simulation study of the interactions between long-range process and short-range statistical variability in a 14-nm technology node silicon-on-insulator FinFET. First, the individual and combined impact of the relevant variability sources, including random discrete dopants, fin line edge roughness (LER), gate LER, and metal gate granularity are studied for the nominal 20-nm physical gate-length FinFET design. This is followed by a comprehensive study of the interactions of the channel length, fin width and fin height systematic process variations with the combined statistical variability sources. The simulations follow a 3×3×3=27 experiment design that covers the process variability space, and 1000 statistical simulations are carried out at each node of the experiment. Both metal-gate-first and metal-gate-last technologies are considered. It is found that statistical variability is significantly dependent on the process-induced variability. The applicability of the Pelgrom law to the FinFET statistical variability, subject to long-range process variations, is also examined. Mismatch factor is strongly dependent on the process variations.

A 1 MB Cache Subsystem Prototype With 1.8 ns Embedded DRAMs in 45 nm SOI CMOS

We describe a single voltage supply, 1 MB cache subsystem prototype that integrates 2 GHz embedded DRAM (eDRAM) macros with on-chip word-line voltage supply generation , a 4 Kb one-time-programmable read-only memory (OTPROM) for redundancy and repair control, on-chip OTPROM programming voltage generation, clock generation and distribution, array built-in self-test circuitry (ABIST), user logic and pervasive logic. The eDRAM employs a programmable pipeline, achieving 1.8 ns latency, and features concurrent refresh capability.

Floating body effects in partially-depleted SOI CMOS circuits

This paper presents a detailed study on the impact of floating body in partially-depleted (PD) SOI MOSFET on various digital VLSI CMOS circuit families. The parasitic bipolar effect resulting from the floating body is shown to degrade the circuit noise margin and stability in general. In certain dynamic circuits and wide multiplexers, the parasitic bipolar effect is shown to cause logic state error if not properly accounted for.

Variability Aware Simulation Based Design- Technology Cooptimization (DTCO) Flow in 14 nm FinFET/SRAM Cooptimization

In this paper, we use an automated tool flow in a 14 nm CMOS fin-shaped field-effect transistor (FinFET)/ static random access memory (SRAM) simulation-based design-technology cooptimization (DTCO) including both process-induced and intrinsic statistical variabilities. A 22 nm FinFET CMOS technology is used to illustrate the sensitivity to process-induced fin shape variation and to motivate this paper. Predictive Technology Computer Aided Design (TCAD) simulations have been carried out to evaluate the transistor performance ahead of silicon. Draft-diffusion simulations calibrated to the ensemble Monte Carlo simulation results are used to explore the process and the statistical variability space. This has been enabled by the automation of the tool flow and the dataset handling. The interplay between the process and the statistical variability has been examined in details. A two-stage compact model strategy is used to capture the interplay between process and statistical variability. To close the DTCO loop, the static noise margin and write noise margin sensitivity to cell design parameters and variability in FinFET-based SRAM designs are studied in details.

Statistical Variability and Reliability and the Impact on Corresponding 6T-SRAM Cell Design for a 14-nm Node SOI FinFET Technology

This paper presents an evaluation of 14-nm SOI FinFET CMOS SRAM codesign techniques in the presence of statistical variability and reliability impact. As statistical variability sources random discrete dopants, gate-edge roughness, fi-edge roughness, metal-gate granularity and random interface trapped charges in N/PBTI are considered.

Circuit Techniques Utilizing Independent Gate Control in Double-Gate Technologies

Independent gate control in double-gate (DG) devices enhances circuit performance and robustness while substantially reducing leakage and chip area. In this paper, we describe circuit techniques which take advantage of the independent biasing properties of symmetrical and asymmetrical DG devices in design. DG circuits at the 25-nm node are analyzed via mixed-mode numerical simulations using Taurus MEDICI. In dynamic circuits, we give examples of conditional keepers, charge sharing prevention scheme, and static keepers. A conditional keeper can dynamically achieve the optimal strength ratio between keeper and evaluation devices by utilizing the front- and backchannel currents in DG devices. A charge sharing mitigation scheme utilizing the back-gate of a logic transistor is then described. Static data retention scheme in dynamic circuits is proposed. A case study for analog applications using a voltage controlled oscillator (VCO) illustrates the specific advantages of DG devices.

Design Considerations for PD/SOI SRAM: Impact of Gate Leakage and Threshold Voltage Variation

We present a critical study of the impact of gate tunneling currents on the yield of 65-nm partially depleted/silicon-on-insulator (PD/SOI) SRAM designs. A new gate leakage monitor structure is developed to obtain device-specific gate leakage characteristics of the SRAM cells. This allows us to explore the design space accurately with reliable process information at an early stage. By relying on supply voltage-dependent analysis, it is shown that the gate-leakage impact on the cell yield can be nonmonotonic and substantial even for nondefective devices. It is also shown that design optimizations such as increased operating voltages or shorter hierarchical bitline architecture can help alleviate the gate-leakage impact on yield. Mixture importance sampling is used to estimate yield in terms of cell writability and stability. Threshold voltage variations to model random fluctuation effects are extrapolated from hardware results.

Low-Power High-Performance Asymmetrical Double-Gate Circuits Using Back-Gate-Controlled Wide-Tunable-Range Diode Voltage

This paper presents a new power-reduction scheme using a back-gate-controlled asymmetrical double-gate device with robust data-retention capability for high-performance logic/SRAM power gating or variable/dynamic supply applications. The scheme reduces the transistor count, area, and capacitance in the header/footer device and provides a wide range of virtual ground (GND) or supply voltage. Physical analysis and numerical mix-mode device/circuit-simulation results confirm that the proposed scheme can be applied to low-power high-performance circuit applications in 65-nm technology node and beyond. Variable/dynamic supply or GND voltage using the proposed scheme improves read and write margins in scaled SRAM without degrading read and write performance.

A low-overhead virtual rail technique for SRAM leakage power reduction

We propose a virtual supply rail control technique that reduces SRAM leakage. This method encompasses a cell-based image, serial tiling, pitch matching, small drive device overhead, and controlled power-on currents while incurring small circuit overhead. A virtual rail cell contains both the sleep transistor fingers and input/output drive transistors. The usual overhead associated with the drive circuit that controls the sleep transistors is significantly reduced due to reduced wire load and improved drive efficiency. This technique provides gradual power-on characteristics and good signal slews while effectively mitigating leakage current, maintaining read/write speed and achieving power-on latency compatible with high-performance designs.

TCAD/Physics-Based Analysis of High-Density Dual-BOX FD/SOI SRAM Cell With Improved Stability

This paper presents a new SRAM cell using a global back-gate bias scheme in dual buried-oxide (BOX) FD/SOI CMOS technologies. The scheme uses a single global back-gate bias for all cells in the entire columns or subarray, thereby reducing the area penalty. The scheme improves 6T SRAM standby leakage, read stability, write ability, and read/write performance. The basic concept of the proposed scheme is discussed based on physical analysis/equation to facilitate device parameter optimization for SRAM cell design in back-gated FD/SOI technologies. Numerical 2-D mixed-mode device/circuit simulation results validate the merits and advantages of the proposed scheme.