The requirement of partial underfilling of flip-chips in certain heterogeneously integrated packages could adversely affect the fatigue life of the micro-solder bumps. We performed numerical simulations to show that the underfilling of the surrounding regions of micro-bumps is necessary to have a comparable fatigue life as those of the full underfill case. The effect of underfill away from the micro-bumps is insignificant on their fatigue life. In the case of partial underfilling with some bumps without surrounding underfill, they become critical with significantly lower life as compared to the micro-bumps surrounded by underfill.

Researcher/Author:  Sasi Kumar Tippabhotla, Lin Ji 

Published in:  2023 IEEE 73rd Electronic Components and Technology Conference (ECTC)

To download the paper, please proceed to:  10.1109/ECTC51909.2023.00042

The RF design for the wire bond and flip-chip Power Amplifier (PA) MMIC on the High Resistivity (HiR) Si-interposer are presented in this paper. The HiR Si-interposer is to support multiple off-the-shelf RF and Baseband ICs for complex advanced RF frontend modules using heterogeneous integration. A two-sided thermal cooling solution is adopted for this high-performance integration architecture. The high-power dissipation MMIC is integrated using flip-chip assembly so that the heat can be dissipated through the top heat spreader. For the other ICs, they are integrated using wire bond assembly so that their heat will be dissipated through the bottom HiR Si-interposer.

Researcher/Author: Teck Guan Lim,Lin Zho, Sasi Kumar Tippabhotia, in Lin, Jong Ming Ching, Jia Qi Wu, Tang Gong Yue, Eva Wai Leong, Yong Chyn Ng, King Jien Chui, Wei Jia Lu, Chee Heng Goh, Sek Lin Pek & Jin Wei Agnes Loh

Published in: 2023 IEEE 73rd Electronic Components and Technology Conference (ECTC)

To download the paper, please proceed to: 10.1109/ECTC51909.2023.00315

We have successfully demonstrated, low-thermal budget oxide-based FETs with a record I D,max of 790μA/μm at V DS = 1V, an enhancement-mode operation (V DH >0), S.S. <90 mV/dec., and DIBL ~20mV/V at an ultra-scaled channel length LCH CH of 50 nm. This is enabled by an optimized InSnO x -InGaZnO x hetero-junction channel to achieve channel defect self-compensation [1]. This approach overcomes the fundamental issue of negative VTH seen in n-type oxide FETs due to donor-type channel oxygen vacancy (Vo) and the limited tunability of gate metal work function. Through our ITO-IGZO channel and defect self-compensation approach, our transistor effective mobility (μeff) is boosted to 110 cm2/V⋅s with the channel thickness (TCH) scaled down to 4 nm. This unique T CH -independent mobility behavior is not observed for IGZO or ITO mono-channel FETs. With such enhancement, our ITO-IGZO FETs exhibit the best-in-class mobility among oxide-based FETs, and are competitive to unstrained Silicon thin film and SOI FETs, while being compatible with sub- 400 °C back-end-of-line (BEOL) processes.

Researcher/Author:  Sonu Hooda, Chun-Kuei Chen, Manohar Lal, Shih-Hao Tsai
, Evgeny Zamburg , Aaron Voon-Yew Thean

Published in:   IEEE 

To download the paper, please proceed to:  

https://ieeexplore.ieee.org/document/10185266

Competitive-learning-based spiking neural networks are capable of rapid, highly accurate pattern recognition with minimal data through denoising mechanisms provide by adaptive interneuron inhibition. However, hardware implementations of such networks are currently area-inefficient due to the high device count require to execute dual excitatory-inhibitory synapses. To mitigate this, n-/p- reconfigurable tungsten diselenide memtransistors is introduced that can execute excitatory and inhibitory synapses in a highly compact bio-inspired feature extractor hardware architecture. The reconfigurability is realized through a dual mode memory device with a flash-memory-like floating-gate for n-/p- programing and a memristor-like selenium vacancy-based resistive switching that varies in memristive output with majority carrier modulation. Through a device-system codesign, an effective 27% device count reduction in the peripheral circuits is achieved , which ameliorates circuit component congestion and circuit complexity. Compared to the prevalent winner-takes-all approach, the proposed machine learning with adaptive interneuron inhibition achieves high-accuracy convergence with up to five times smaller training dataset. This accelerated learning can potentially enable edge-artificial intelligence (AI) processors capable of ultra-low-energy training with limited data.

Researcher/Author:  Jin Feng Leong, Zihang Fang, Maheswari Sivan, Jieming Pan, Baoshan Tang,
Evgeny Zamburg, and Aaron V-Y Thean

Published in:  Advanced Functional Materials

To download the paper, please 

proceed to:  https://doi.org/10.1002/adfm.202302949

Researcher/Author: Guoqiang Xu, Xue Zhou, Ying Li, Qitao Cao, Weijin Chen, Yunfeng Xiao, Lan Yang, and Cheng-Wei Qiu

Publisher: Physical Review Letters vol. 130 Issue 26 

To download the paper, click here. 

The quantized bulk quadrupole moment has so far revealed a non-trivial boundary state with lower-dimensional topological edge states and in-gap zero-dimensional corner modes. In contrast to photonic implementations, state-of-the-art strategies for topological thermal metamaterials struggle to achieve such higher-order hierarchical features. This is due to the absence of quantized bulk quadrupole moments in thermal diffusion fundamentally prohibiting possible band topology expansions. Here, we report a recipe for generating quantized bulk quadrupole moments in fluid heat transport and observe the quadrupole topological phases in non-Hermitian thermal systems. Our experiments show that both the real- and imaginary-valued bands exhibit the hierarchical features of bulk, gapped edge and in-gap corner states—in stark contrast to the higher-order states observed only on real-valued bands in classical wave fields. Our findings open up unique possibilities for diffusive metamaterial engineering and establish a playground for multipolar topological physics.

Researcher/Author: Guoqiang Xu^1,5, Xue Zhou^2,5, Shuihua Yang^1,5, Jing Wu^3,4 & Cheng-Wei Qiu¹

Published in: Nature Communications volume | (2023)  14, Article number: :3252

To download the paper, please proceed to: https://www.nature.com/articles/s41467-023-39117-w

The estimation of the direction of arrival (DOA) for receiving cylindrical antenna arrays is presented. The analysis uses the Cramer-Rao lower bound (CRLB), which provides the best unbiased estimation for minimizing the residual noise. First, the CRLB for conformal surfaces is derived. Then the method is applied to case studies to gauge the difference in the performance of cylindrical arrays compared to a planar array. The presented approach can help designers of cylindrical conformal arrays to optimize the antenna performance.

Researcher/Author:  Jiahao Wang, Peizhuo Yang and Koen Mouthaan

Published in:  IEEE

To download the paper, please 

proceed to:  https://ieeexplore.ieee.org/xpl/conhome/10132843/proceeding

Researcher/Author:  Yingchao Zhang, Yurong Tan, Jiazheng Lao, Huajian Gao and Jing Yu

Publisher:  ACS Nano 2023

To download the paper, click here. 

DOI:10.1021/acsnano.3c02897

In this work, Shine Thrust 3 researchers under the supersion of principal investigator, Prof Aaron Thean of NUS Department of Electrical and Computer Engineering developed an anneal-free back-end-of-line (BEOL) process for ferroelectric hafnium zirconium oxide (HZO)/indium gallium zinc oxide (IGZO)-based ferroelectric field-effect transistor (FeFET), suitable for in-memory computing. The novel anneal-free BEOL FeFET presented in this work stunningly achieves a competitive performance under a record-low thermal budget. Ultra-low subthreshold swing (SS) of 66.2 mV/dec, large on/off current ratio (ION/IOFF) of >107 , large memory window (MW) of >1.7 V, high endurance of >107 cycles without significant degradation are obtained.

Researcher/Author: Shih-Hao Tsai, Zhonghua Li, Ma Mo Mo Ei Phyu, Zihang Fang

Published in: 2023 7th IEEE Electron Devices Technology & Manufacturing Conference (EDTM)

For paper download, goto: Back-End-of-Line-Compatible Anneal-Free Ferroelectric Field-Effect Transistor (researchgate.net)

Maintaining the concentrations of various ions in body fluids is critical to all living organisms. In this contribution, we designed  a flexible microneedle patch coupled electrode array (MNP-EA) for the in situ multiplexed detection of ion species (Na+ , K+ , Ca2+, and H+ ) in tissue interstitial fluid (ISF). The microneedles (MNs) are mechanically robust for skin or cuticle penetration (0.21 N/needle) and highly swellable to quickly extract sufficient ISF onto the ion-selective
electrochemical electrodes (∼6.87 μL/needle in 5 min). The potentiometric sensor can simultaneously detect these ion species with nearly Nernstian response in the ranges wider enough for diagnosis purposes (Na+ : 0.75−200 mM, K+ : 1−128 mM, Ca2+: 0.25−4.25 mM, pH: 5.5−8.5). The in vivo experiments on mice, humans, and plants demonstrate the feasibility of MNP-EA for timely and convenient diagnosis of ion imbalances with minimal invasiveness. This transdermal sensing platform shall be instrumental to home-based diagnosis and health monitoring of chronic diseases and is also promising for smart agriculture and the study of plant biology

Researcher/Author: Dan Dan Zhu, Yu Rong Tan, Le Wen Zheng,  Jia Zheng Lao, Ji Yang Liu, Jing Yu and Peng Chen

Published in:  ACS Appl. Mater. Interfaces 2023

To download the paper, please proceed to: 10.1021/acsami.3c00573 

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues enroute to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Researcher/Author:
Yifei Luo, Mohammad Reza Abidian, Jong-yun Ahn, Deji Akinwande, Anne M. Andrews, Markus Antonietti, Zhenan Bao, Magnus Berggren, Christopher A. Berkey, Christopher John Bettinger, Jun Chen, Peng Chen, Wenlong Cheng, Xu Cheng, Seon-Jin Choi, Alex Chortos, Canan Dagdeviren, Reinhold H. Dauskardt, Chong-an Di, Michael D. Dickey, Xiangfeng Duan, Antonio Facchetti, Zhiyong Fan, Yin Fang, Jianyou Feng, Xue Feng, Huajian Gao, Wei Gao, Xiwen Gong, Chuan Fei Guo, Xiaojun Guo, Martin C. Hartel, Zihan He, John S. Ho, Youfan Hu, Qiyao Huang, Yu Huang, Fengwei Huo, Muhammad M. Hussain, Ali Javey, Unyong Jeong, Chen Jiang, Xingyu Jiang, Jiheong Kang, Daniil Karnaushenko, Ali Khademhosseini, Dae-Hyeong Kim, Il-Doo Kim, Dmitry Kireev, Lingxuan Kong, Chengkuo Lee, Nae-Eung Lee, Pooi See Lee, Tae-Woo Lee, Fengyu Li, Jinxing Li, Cuiyuan Liang, Chwee Teck Lim, Yuanjing Lin, Darren J. Lipomi, Jia Liu, Kai Liu, Nan Liu, Ren Liu, Yuxin Liu, Yuxuan Liu, Zhiyuan Liu, Zhuangjian Liu, Xian Jun Loh, Nanshu Lu, Zhisheng Lv, Shlomo Magdassi, George G. Malliaras, Naoji Matsuhisa, Arokia Nathan, Simiao Niu, Jieming Pan, Changhyun Pang, Qibing Pei, Huisheng Peng, Dianpeng Qi, Huaying Ren, John A. Rogers, Aaron Rowe, Oliver G. Schmidt, Tsuyoshi Sekitani, Dae-Gyo Seo, Guozhen Shen, Xing Sheng, Qiongfeng Shi, Takao Someya, Yanlin Song, Eleni Stavrinidou, Meng Su, Xuemei Sun, Kuniharu Takei, Xiao-Ming Tao, Benjamin C. K. Tee, Aaron Voon-Yew Thean, Tran Quang Trung, Changjin Wan, Huiliang Wang, Joseph Wang, Ming Wang, Sihong Wang, Ting Wang, Zhong Lin Wang, Paul S. Weiss, Hanqi Wen, Sheng Xu, Tailin Xu, Hongping Yan, Xuzhou Yan, Hui Yang, Le Yang, Shuaijian Yang, Lan Yin, Cunjiang Yu, Guihua Yu, Jing Yu, Shu-Hong Yu, Xinge Yu, Evgeny Zamburg, Haixia Zhang, Xiangyu Zhang, Xiaosheng Zhang, Xueji Zhang, Yihui Zhang, Yu Zhang, Siyuan Zhao, Xuanhe Zhao, Yuanjin Zheng, Yu-Qing Zheng, Zijian Zheng, Tao Zhou, Bowen Zhu, Ming Zhu, Rong Zhu, Yangzhi Zhu, Yong Zhu, Guijin Zou, and Xiaodong Chen*

Published in: ACS Nano 2023, 17, 6, 5211–5295

https://doi.org/10.1021/acsnano.2c12606

Stretchable hybrid devices have enabled high-fidelity implantable and on-skin monitoring of physiological signals. These devices typically contain soft modules that match the mechanical requirements in humans and soft robots, rigid modules containing Si-based microelectronics and protective encapsulation modules. To make such a system mechanically compliant, the interconnects between the modules need to tolerate stress concentration that may limit their stretching and ultimately cause debonding failure. Here, we report a universal interface that can reliably connect soft, rigid and encapsulation modules together to form robust and highly stretchable devices in a plug-and-play manner. The interface, consisting of interpenetrating polymer and metal nanostructures, connects modules by simply pressing without using pastes. Its formation is depicted by a biphasic network growth model. Soft–soft modules joined by this interface achieved 600% and 180% mechanical and electrical stretchability, respectively. Soft and rigid modules can also be electrically connected using the above interface. Encapsulation on soft modules with this interface is strongly adhesive with an interfacial toughness of 0.24 N mm−1. As a proof of concept, we use this interface to assemble stretchable devices for in vivo neuromodulation and on-skin electromyography, with high signal quality and mechanical resistance. We expect such a plug-and-play interface to simplify and accelerate the development of on-skin and implantable stretchable devices.

Researcher/Author: Ying Jiang (NTU), Shaobo Ji (NUS), Jing Sun (SIAT/CAS), Jianping Huang (SIAT/CAS), Yuanheng Li, Guijin Zou (A*STAR IHPC), Teddy Salim (NTU), Changxian Wang (NTU), Wenlong Li (A*STAR IME), Haoran Jin (NTU/NUS), Jie Xu (Standford), Sihong Wang (Stanford), Ting Lei (Standford), Xuzhou Yan (Stanford), Wendy Yen Xian Peh (NUS), Shih-Cheng Yen (NUS), Zhihua Liu (NUS), Mei Yu (SIAT/CAS), Hang Zhao (SIAT/CAS), Zechao Lu (SIAT/CAS), Guanglin Li (SIAT/CAS), Huajian Gao (A*STAR IHPC), Zhiyuan Liu (SIAT/CAS), Zhenan Bao (Standford) & Xiaodong Chen (NTU)

Nature volume 614, pages456–462 (2023)
https://www.nature.com/articles/s41586-022-05579-z

In this article, we demonstrate a low-thermal budget defect-engineered process to achieve top-gated (TG) oxide–semiconductor ferroelectric field-effect transistors (FeFETs). The demonstrated TG FeFETs, with the channel length scaled down to 40 nm, exhibit a highly stabilized ferroelectric memory window (MW) of 2 V and a high current ON/OFF ratio of 106. This is achieved by an engineered InGaZnOx (IGZO) and InSnOx (ITO) heterojunction channel that produces the defect self-compensation effect to passivate the intrinsic oxygen-deficient defects, existing in the indium-gallium-zinc-oxide (IGZO) channel interface and bulk. Effective interface/bulk defects passivation with good control of defect-induced channel carrier concentration has been notoriously difficult to achieve. Hence, realizing performant TG oxide-based FeFETs with back-end-of-line (BEOL) thermal budget constraints remains a fundamental challenge. Our study shows that heterojunction channel engineering on FETs and FeFETs can be a reliable solution to overcome this challenge. With such a technique, we can now enable double-gated (DG) ITO–IGZO FeFET and FETs. Such devices can enable BEOL-compatible reconfigurable nonvolatile logic switches that provide extremely low off-state leakage, high switch conductance ratio, and memory read-write disturb-free features.

Researcher/Author:
Aaron Voon-Yew Thean, Chun-Kuei Chen, Sonu Hooda, Zihang Fang, Manohar Lal, Zefeng Xu, Jieming Pan, Shih-Hao Tsai, and Evgeny Zamburg 

Published in: IEEE Transactions on Electron Devices ( Volume: 70, Issue: 4, April 2023) International Electron Devices Meeting (IEDM)
Page(s):  2098 – 2105

https://ieeexplore.ieee.org/document/10043682

If Si CMOS for massive M3D is difficult due to need for high-thermal-budget processes, are there solutions that are beyond Si? In this article, we discuss two low-thermal budget approaches: Oxide Semiconductor and 2D Materials for M3D integration. By reviewing some of our recent work with IGZO-based transistors and memories, followed by our investigation of the 2D material opportunities for 3D memories, we highlight the need for new low-thermal-budget additive techniques for heterogenous multi-material integration as well as low-temperature material modification. Given the unlikelihood of “perfect materials”, new system architecture-material-device co-design intervention will be essential to capitalize on the specific trade-offs of the components.

Researcher/Author: 
Aaron Voon-Yew Thean^†, Evgeny Zamburg^†, Shih-Hao Tsai, Chun-Kuei Chen, Maheswari Sivan, Baoshan Tang, Sonu Hooda, Zihang Fang, Jieming Pan, Jinfeng Leong, and Hasita Veluri. 

Published in: 2022 International Electron Devices Meeting (IEDM)

https://ieeexplore.ieee.org/document/10019501