Chenming Calvin Hu

Bio: Chenming Calvin Hu is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: MOSFET & Semiconductor device modeling. The author has an hindex of 3, co-authored 4 publications receiving 122 citations.

BSIM—SPICE Models Enable FinFET and UTB IC Designs

Abstract: Two turn-key surface potential-based compact models are developed to simulate multigate transistors for integrated circuit (IC) designs. The BSIM-CMG (common-multigate) model is developed to simulate double-, triple-, and all-around-gate FinFETs and it is selected as the world's first industry-standard compact model for the FinFET. The BSIM-IMG (independent-multigate) model is developed for independent double-gate, ultrathin body (UTB) transistors, capturing the dynamic threshold voltage adjustment with back gate bias. Starting from long-channel devices, the basic models are first obtained using a Poisson-carrier transport approach. The basic models agree with the results of numerical two-dimensional device simulators. The real-device effects then augment the basic models. All the important real-device effects, such as short-channel effects (SCEs), quantum mechanical confinement effects, mobility degradation, and parasitics are included in the models. BSIM-CMG and BSIM-IMG have been validated with hardware silicon-based data from multiple technologies. The developed models also meet the stringent quality assurance tests expected of production level models.

BSIM compact MOSFET models for SPICE simulation

Abstract: Continuous technology advancements have forced MOSFET architecture to evolve from bulk to SOI to multigate MOSFETs. BSIM compact models have helped circuit designers to realize their designs first time correct using accurate physical models used in SPICE simulation. BSIM3 and BSIM4 are threshold voltage based bulk MOSFET models while BSIM6 is charge based bulk MOSFET model, which include physical effects such as mobility degradation, current saturation, high frequency models etc. BSIM6 has been developed especially to address symmetry around Vds = 0, thus providing smooth higher order derivatives. BSIM-CMG is a CMC standard surface potential based model for common symmetric double, triple, quadruple and surround gate (nanowire) MOSFETs. Long channel DIBL also called Drain-Induced Threshold Shift (DITS) effect and asymmetric charge weighing factor etc. have been recently included in it. BSIM-IMG is a surface potential based model to simulate ultra-thin body devices such as UTBSOI but also other thin body devices such as MOS2 transistor.

2D MOSFET operation of a fully-depleted bulk MoS 2 at quasi-flatband back-gate

Abstract: In this paper, 2D MOSFET operation of a fully-depleted double-gate bulk MoS 2 is studied at a quasi-flatband of the back-gate for the first time. Several key device parameters such as equivalent oxide thickness (EOT), carrier concentration, flatband voltage, dielectric constant and carrier mobility were extracted from I-V and C-V characteristics and at room temperature. In a similar operation to the inversion-mode SOI MOSFETs in [1], the backgate was used to keep a sheet of mobile charges on the flake back-side by its quasi-flatband operation at a fixed voltage (0 V). Afterward, the top-gate was used as the active gate to perform mobile charge accumulation or depletion in the channel. Fig. 1 shows the device architecture together with the high frequency R-C equivalent circuit model for this underlap gate architecture. Fig. 2 represents the top-view microscope picture of the fabricated MoS 2 bulk MOSFET with a flake thickness of 38 nm, measured by AFM. The fabrication steps include mechanical exfoliation of MoS 2 crystals on a 260 nm thick oxidized Si substrate, e-beam lithography to make S/D pads, 50 nm Ni by thermal evaporation and lift-off, gate patterning, high-k/metal-gate stack deposition (1 nm of SiO x by thermal evaporation, 11 nm of ZrO 2 by ALD deposition at 105 °C, 30 nm of Ni by thermal evaporation) and lift-off. The measurements were done at room temperature using an Agilent B1500A Semiconductor Parameter Analyzer. Fig. 3 shows its I d -V g , reporting a subthreshold slope of 110 mV/dec. and I on /I off of ∼1×105, both at V ds =100 mV.

Analysis and modeling of vertical non-uniform doping in bulk MOSFETs for circuit simulation

Abstract: We present an efficient approach to model the effects of vertical non-uniform doping in bulk MOSFETs. The impact of vertical non-uniform doping on device characteristics is analyzed through systematic TCAD simulations. The qualitative nature of the observed effects is also confirmed by the experimental data available in the literature. A modeling methodology for these effects is developed on BSIM6 model framework. The proposed model is in good agreement with the TCAD simulations.

FinFETs: From Devices to Architectures

Abstract: Since Moore’s law driven scaling of planar MOSFETs faces formidable challenges in the nanometer regime, FinFETs and Trigate FETs have emerged as their successors. Owing to the presence of multiple (two/three) gates, FinFETs/Trigate FETs are able to tackle short-channel effects (SCEs) better than conventional planar MOSFETs at deeply scaled technology nodes and thus enable continued transistor scaling. In this paper, we review research on FinFETs from the bottommost device level to the topmost architecture level. We survey different types of FinFETs, various possible FinFET asymmetries and their impact, and novel logic-level and architecture-level tradeoffs offered by FinFETs. We also review analysis and optimization tools that are available for characterizing FinFET devices, circuits, and architectures.

BSIM6: Analog and RF Compact Model for Bulk MOSFET

Abstract: BSIM6 is the latest industry-standard bulk MOSFET model from the BSIM group developed specially for accurate analog and RF circuit designs. The popular real-device effects have been brought from BSIM4. The model shows excellent source-drain symmetry during both dc and small signal analysis, thus giving excellent results during analog and RF circuit simulations, e.g., harmonic balance simulation. The model is fully scalable with geometry, biases, and temperature. The model has a physical charge-based capacitance model including polydepletion and quantum-mechanical effect thereby giving accurate results in small signal and transient simulations. The BSIM6 model has been extensively validated with industry data from 40-nm technology node.

Reliability-aware design to suppress aging

Abstract: Due to aging, circuit reliability has become extraordinary challenging. Reliability-aware circuit design flows do virtually not exist and even research is in its infancy. In this paper, we propose to bring aging awareness to EDA tool flows based on so-called degradation-aware cell libraries. These libraries include detailed delay information of gates/cells under the impact that aging has on both threshold voltage (V th ) and carrier mobility (μ) of transistors. This is unlike state of the art which considers V th only. We show how ignoring s degradation leads to underestimating guard-bands by 19% on average. Our investigation revealed that the impact of aging is strongly dependent on the operating conditions of gates (i.e. input signal slew and output load capacitance), and not solely on the duty cycle of transistors. Neglecting this fact results in employing insufficient guard-bands and thus not sustaining reliability during lifetime. We demonstrate that degradation-aware libraries and tool flows are indispensable for not only accurately estimating guardbands, but also efficiently containing them. By considering aging degradations during logic synthesis, significantly more resilient circuits can be obtained. We further quantify the impact of aging on the degradation of image processing circuits. This goes far beyond investigating aging with respect to path delays solely. We show that in a standard design without any guardbanding, aging leads to unacceptable image quality after just one year. By contrast, if the synthesis tool is provided with the degradation-aware cell library, high image quality is sustained for 10 years (even under worst-case aging and without a guardband). Hence, using our approach, aging can be effectively suppressed.

All WSe2 1T1R resistive RAM cell for future monolithic 3D embedded memory integration.

Abstract: 3D monolithic integration of logic and memory has been the most sought after solution to surpass the Von Neumann bottleneck, for which a low-temperature processed material system becomes inevitable. Two-dimensional materials, with their excellent electrical properties and low thermal budget are potential candidates. Here, we demonstrate a low-temperature hybrid co-integration of one-transistor-one-resistor memory cell, comprising a surface functionalized 2D WSe2 p-FET, with a solution-processed WSe2 Resistive Random Access Memory. The employed plasma oxidation technique results in a low Schottky barrier height of 25 meV with a mobility of 230 cm2 V−1 s−1, leading to a 100x performance enhanced WSe2 p-FET, while the defective WSe2 Resistive Random Access Memory exhibits a switching energy of 2.6 pJ per bit. Furthermore, guided by our device-circuit modelling, we propose vertically stacked channel FETs for high-density sub-0.01 μm2 memory cells, offering a new beyond-Si solution to enable 3-D embedded memories for future computing systems. Designing efficient, scalable and low-thermal-budget 2D Materials for 3D integration remains a challenge. Here, the authors report the development of a hybrid-(solution-processed-exfoliated) integration of 2D Material based 1T1R which uses a multilayer WSe2 p-FET and a multilayer printed WSe2 RRAM.