May 30, 2023

[PhD Thesis] Digital-based analog processing in nanoscale CMOS ICs for IoT applications

Digital-based analog processing in nanoscale CMOS ICs for IoT applications
PhD Cadndiate: Pedro Filipe Leite Correia De Toledo
Universidade Federal do Rio Grande do Sul. Instituto de Informática
Programa de Pós-Graduação em Microeletrônica.
Advisor: Klimach, Hamilton Duarte
Co-advisor: Crovetti, Paolo Stefano

Abstract: The Internet-of-Things (IoT) concept has been opening up a variety of applications, such as urban and environmental monitoring, smart health, surveillance, and home automation. Most of these IoT applications require more and more power/area efficient Complemen ary Metal–Oxide–Semiconductor (CMOS) systems and faster prototypes (lower time-to market), demanding special modifications in the current IoT design system bottleneck: the analog/RF interfaces. Specially after the 2000s, it is evident that there have been significant improvements in CMOS digital circuits when compared to analog building blocks. Digital circuits have been taking advantage of CMOS technology scaling in terms of speed, power consumption, and cost, while the techniques running behind the analog signal processing are still lagging. To decrease this historical gap, there has been an increasing trend in finding alternative IC design strategies to implement typical analog functions exploiting Digital in-Concept Design Methodologies (DCDM). This idea of re-thinking analog functions in digital terms has shown that Analog ICs blocks can also avail of the feature-size shrinking and energy efficiency of new technologies. This thesis deals with the development of DCDM, demonstrating its compatibility for Ultra-Low-Voltage (ULV) and Power (ULP) IoT applications. This work proves this statement through the proposing of new digital-based analog blocks, such as an Operational Transconductance Amplifiers (OTAs) and an ac-coupled Bio-signal Amplifier (BioAmp). As an initial contribution, for the first time, a silicon demonstration of an embryonic Digital-Based OTA (DB-OTA) published in 2013 is exhibited. The fabricated DB-OTA test chip occupies a compact area of 1,426 µm2 , operating at supply voltages (VDD) down to 300 mV, consuming only 590 pW while driving a capacitive load of 80pF. With a Total Harmonic Distortion (THD) lower than 5% for a 100mV input signal swing, its measured small-signal figure of merit (FOMS) and large-signal figure of merit (FOML) are 2,101 V −1 and 1,070, respectively. To the best of this thesis author’s knowledge, this measured power is the lowest reported to date in OTA literature, and its figures of merit are the best in sub-500mV OTAs reported to date. As the second step, mainly due to the robustness limitation of previous DB-OTA, a novel calibration-free digital-based topology is proposed, named here as Digital OTA (DIG OTA). A 180-nm DIGOTA test chip is also developed exhibiting an area below the 1000 µm2 wall, 2.4nW power under 150pF load, and a minimum VDD of 0.25 V. The proposed DIGOTA is more digital-like compared with DB-OTA since no pseudo-resistor is needed. As the last contribution, the previously proposed DIGOTA is then used as a building block to demonstrate the operation principle of power-efficient ULV and ultra-low area (ULA) fully-differential, digital-based Operational Transconductance Amplifier (OTA), suitable for microscale biosensing applications (BioDIGOTA) such as extreme low area Body Dust. Measured results in 180nm CMOS confirm that the proposed BioDIGOTA can work with a supply voltage down to 400 mV, consuming only 95 nW. The BioDIGOTA layout occupies only 0.022 mm2 of total silicon area, lowering the area by 3.22X times compared to the current state of the art while keeping reasonable system performance, such as 7.6 Noise Efficiency Factor (NEF) with 1.25 µVRMS input-referred noise over a 10 Hz bandwidth, 1.8% of THD, 62 dB of the common-mode rejection ratio (CMRR) and 55 dB of power supply rejection ratio (PSRR). After reviewing the current DCDM trend and all proposed silicon demonstrations, the thesis concludes that, despite the current analog design strategies involved during the analog block development

Fig: a) analog design octagon; b) gm/ID·fT versus the inversion coefficient IC, λc is the parameter corresponding to the fraction of the channel in which the carrier drift velocity reaches the saturated velocity over a portion of the channel geometrical length; c) Performance difference between analog and digital blocks over time; d) Area reduction over the years of the bitcell SRAM, OTA and bandgap reference

May 26, 2023

[paper] Chip-Chat

Jason Blocklove, Siddharth Garg, Ramesh Karri, and Hammond Pearce^
Chip-Chat: Challenges and Opportunities in Conversational Hardware Design
arXiv preprint arXiv:2305.13243 [cs.LG] 22 May 2023

New York University, NY USA
^University of New South Wales Sydney, Australia

Abstract: Modern hardware design starts with specifications provided in natural language. These are then translated by hardware engineers into appropriate Hardware Description Languages (HDLs) such as Verilog before synthesizing circuit elements. Automating this translation could reduce sources of human error from the engineering process. But, it is only recently that artificial intelligence (AI) has demonstrated capabilities for machine-based end-to-end design translations. Commercially available instruction-tuned Large Language Models (LLMs) such as OpenAI’s ChatGPT and Google’s Bard claim to be able to produce code in a variety of programming languages; but studies examining them for hardware are still lacking. In this work, we thus explore the challenges faced and opportunities presented when leveraging these recent advances in LLMs for hardware design. Using a suite of 8 representative benchmarks, we examined the capabilities and limitations of the state of the art conversational LLMs when producing Verilog for functional and verification purposes. Given that the LLMs performed best when used interactively, we then performed a longer, fully conversational case study where a hardware engineer co-designed a novel 8-bit accumulator-based microprocessor architecture. We sent the benchmarks and processor to tapeout in a Skywater 130nm shuttle, meaning that these ‘Chip-Chats’ resulted in what we believe to be the world’s first wholly-AI-written HDL for tapeout.
Fig: Processor synthesis information - Above (a) Components. Left: (b) Final processorGDS render by ‘kLayout’, I/O ports on left side, grid lines = 0.001 um.

Opportunities: Still, when the human feedback is provided to the more capable ChatGPT-4 model, or it is used to co-design, the language model seems to be a ‘force multiplier’, allowing for rapid design space exploration and iteration. In general, ChatGPT-4 could produce functionally correct code, which could free up designer time when implementing common modules. Potential future work could involve a larger user study to investigate this potential, as well as the development of conversational LLMs specific to hardware design to improve upon the results.

[paper] integrated PD SOI CMOS microcantilever biosensor

Yi Liu, Yuan Tian, Cong Lin, Jiahao Miao & Xiaomei Yu*
A monolithically integrated microcantilever biosensor 
based on partially depleted SOI CMOS technology
Microsystems & Nanoengineering volume 9, Article number: 60 (2023)
DOI: 10.1038/s41378-023-00534-y

* School of Integrated Circuits, Peking University, National Key Laboratory of Science and Technology on Micro/Nano Fabrication, Beijing, 100871, China

Abstract: This paper presents a monolithically integrated aptasensor composed of a piezoresistive microcantilever array and an on-chip signal processing circuit. Twelve microcantilevers, each of them embedded with a piezoresistor, form three sensors in a Wheatstone bridge configuration. The on-chip signal processing circuit consists of a multiplexer, a chopper instrumentation amplifier, a low-pass filter, a sigma-delta analog-to-digital converter, and a serial peripheral interface. Both the microcantilever array and the on-chip signal processing circuit were fabricated on the single-crystalline silicon device layer of a silicon-on-insulator (SOI) wafer with partially depleted (PD) CMOS technology followed by three micromachining processes. The integrated microcantilever sensor makes full use of the high gauge factor of single-crystalline silicon to achieve low parasitic, latch-up, and leakage current in the PD-SOI CMOS. A measured deflection sensitivity of 0.98 × 10−6 nm−1 and an output voltage fluctuation of less than 1 μV were obtained for the integrated microcantilever. A maximum gain of 134.97 and an input offset current of only 0.623 nA were acquired for the on-chip signal processing circuit. By functionalizing the measurement microcantilevers with a biotin-avidin system method, human IgG, abrin, and staphylococcus enterotoxin B (SEB) were detected at a limit of detection (LOD) of 48 pg/mL. Moreover, multichannel detection of the three integrated microcantilever aptasensors was also verified by detecting SEB. All these experimental results indicate that the design and process of monolithically integrated microcantilevers can meet the requirements of high-sensitivity detection of biomolecules.

FIG: a) Micrograph of the fabricated integrated microcantilever sensor IC.
b) SEM photograph of the microcantilever array

Acknowledgements: This research was funded by the National Natural Science Foundation of China (Grant No. 61935001).

Open Access: this article is licensed under a Creative Commons Attribution 4.0 International License 

May 23, 2023

[paper] Schottky Barrier FET at Deep Cryogenic Temperatures

Christian Roemer1,2, Nadine Dersch1, Ghader Darbandy1, Mike Schwarz1,
Yi Han3, Qing-Tai Zhao3, Benjamın Iniguez2 and Alexander Kloes1
Compact Modeling of Schottky Barrier Field-Effect Transistors 
at Deep Cryogenic Temperatures
in Tarragona (Catalonia, Spain) on May 10-12 2023

1 NanoP, TH Mittelhessen - University of Applied Sciences, Giessen, Germany
2 DEEEA, Universitat Rovira i Virgili, Tarragona, Spain
3 Peter-Grunberg-Institute (PGI 9), Forschungszentrum Julich, Germany

Abstract: In this paper, a physics-based DC compact model for Schottky barrier field-effect transistors at deep cryogenic temperatures is presented. The model uses simplified tunneling equations at temperatures of ϑ ≈ 0 K in order to calculate the field emission injection current at the device’s Schottky barriers. The compact model is also compared to and verified by measurements of ultra-thin body and buried oxide SOI Schottky barrier field-effect transistors and is able to capture the signature of resonant tunneling effects in the transfer characteristics.

FIG: Band diagram at the source side Schottky junction (left-hand side). The solid blue line is the conduction band of the channel and the blue dashed line shows the metal’s Fermi energy level. The right-hand side subplot shows the tunneling probability, with the exponential part (red line) and the total probability, including the oscillations (green line).

[paper] GaN HEMTs: Past, development, and future

Haorui Luoab, Wenrui Huaa, Yongxin Guoab,
On large-signal modeling of GaN HEMTs: Past, development, and future
Chip, 2023, 100052
DOI: 10.1016/j.chip.2023.100052.
a Department of Electrical and Computer Engineering, National University of Singapore
b National University of Singapore (Suzhou) Research Institute, China

Abstract : In the past few decades, circuits based on gallium nitride high electron mobility transistor (GaN HEMT) have demonstrated exceptional potential in a wide range of high-power and high-frequency applications, such as the new generation mobile communications, object detection, consumer electronics, etc. As a critical intermediary between GaN HEMT devices and circuit-level applications, GaN HEMT large-signal models play a pivotal role in the design, application and development of GaN HEMT devices and circuits. This review provides an in-depth examination of the advancements in GaN HEMT large-signal modeling in recent decades. Detailed and comprehensive coverage of various aspects of GaN HEMT large-signal model are offered, including large-signal measurement setups, classical formulation methods, model classification, non-ideal effects, etc. In order to better serve follow-up research, this review also explores potential future directions for the development of GaN HEMT large-signal modeling.
FIG : Timeline of some typical GaN HEMT large-signal models.

Funding : This work was supported in part by the National Research Foundation (NRF) of Singapore under Grant NRF-CRP17-2017-08.