Aftab M. Hussain

CMOS‐Technology‐Enabled Flexible and Stretchable Electronics for Internet of Everything Applications

Flexible and stretchable electronics can dramatically enhance the application of electronics for the emerging Internet of Everything applications where people, processes, data and devices will be integrated and connected, to augment quality of life. Using naturally flexible and stretchable polymeric substrates in combination with emerging organic and molecular materials, nanowires, nanoribbons, nanotubes, and 2D atomic crystal structured materials, significant progress has been made in the general area of such electronics. However, high volume manufacturing, reliability and performance per cost remain elusive goals for wide commercialization of these electronics. On the other hand, highly sophisticated but extremely reliable, batch-fabrication-capable and mature complementary metal oxide semiconductor (CMOS)-based technology has facilitated tremendous growth of todays digital world using thin-film-based electronics; in particular, bulk monocrystalline silicon (100) which is used in most of the electronics existing today. However, one fundamental challenge is that state-of-the-art CMOS electronics are physically rigid and brittle. Therefore, in this work, how CMOS-technology-enabled flexible and stretchable electronics can be developed is discussed, with particular focus on bulk monocrystalline silicon (100). A comprehensive information base to realistically devise an integration strategy by rational design of materials, devices and processes for Internet of Everything electronics is offered.

Transformational Silicon Electronics

In todays traditional electronics such as in computers or in mobile phones, billions of high-performance, ultra-low-power devices are neatly integrated in extremely compact areas on rigid and brittle but low-cost bulk monocrystalline silicon (100) wafers. Ninety percent of global electronics are made up of silicon. Therefore, we have developed a generic low-cost regenerative batch fabrication process to transform such wafers full of devices into thin (5 μm), mechanically flexible, optically semitransparent silicon fabric with devices, then recycling the remaining wafer to generate multiple silicon fabric with chips and devices, ensuring low-cost and optimal utilization of the whole substrate. We show monocrystalline, amorphous, and polycrystalline silicon and silicon dioxide fabric, all from low-cost bulk silicon (100) wafers with the semiconductor industrys most advanced high-κ/metal gate stack based high-performance, ultra-low-power capacitors, field effect transistors, energy harvesters, and storage to emphasize the effectiveness and versatility of this process to transform traditional electronics into flexible and semitransparent ones for multipurpose applications.

Flexible and Semi‐Transparent Thermoelectric Energy Harvesters from Low Cost Bulk Silicon (100)

Silicon electronics are at the heart of today’s digital world. Silicon based micro-fabrication technology has unparalleled performance, cost, and yield advantages. However, silicon is brittle and cannot be used for many healthcare and electronic applications. Most living organs are intrinsically of irregular shapes and thus medical electronics intended for implantation on host features such as eye balls or ears need to be fl exible. [ 1 ] Therefore, exploration for a low-cost, simple solution using plastic as substrate and organic materials to fabricate fl exible electronics, like displays and sensors, is on the rise. [ 2–5 ] The basic challenges associated with fl exible electronics compared to precision silicon technology are high thermal budget process incompatibility and inherently low electron mobility. [ 6 ] These two major challenges hinder their potential to integrate high performance devices on a traditional plastic based fl exible platform. With increased world population and concerns about health care, it is important to develop technologies which will be integrated in a benign way to humans or garments capable of collecting and transmitting necessary real-time data to address issues like seizure, heart attacks, etc. [ 7 ] This means high performance silicon-based transistors are required to be implemented on fl exible platforms. Simultaneously, such systems would require ultralow power consumption sourced conveniently from the surrounding environment. Thermoelectric energy harvesters (generators or TEGs) are one of the most pragmatic options to serve as a mobile power source. [ 8 ] Some micrometer-sized TEGs are even commercially available. [ 9–11 ] A few efforts have been made to fabricate them on fl exible substrates like polymide sheet and SU-8 based polymers. [ 12–15 ] Major challenges with these materials are (i) their low melting point making them incompatible for high temperature operation; (ii) their incompatibility for thick fi lm deposition using electrochemical deposition and iii) due to low thermal conductivity ( < 1 W/mK), the temperature cannot drop across the thermocouples. Energy harvesters like TEGs have not

Flexible nanoscale high-performance FinFETs.

With the emergence of the Internet of Things (IoT), flexible high-performance nanoscale electronics are more desired. At the moment, FinFET is the most advanced transistor architecture used in the state-of-the-art microprocessors. Therefore, we show a soft-etch based substrate thinning process to transform silicon-on-insulator (SOI) based nanoscale FinFET into flexible FinFET and then conduct comprehensive electrical characterization under various bending conditions to understand its electrical performance. Our study shows that back-etch based substrate thinning process is gentler than traditional abrasive back-grinding process; it can attain ultraflexibility and the electrical characteristics of the flexible nanoscale FinFET show no performance degradation compared to its rigid bulk counterpart indicating its readiness to be used for flexible high-performance electronics.

Ultrastretchable and Flexible Copper Interconnect‐Based Smart Patch for Adaptive Thermotherapy

Unprecedented 800% stretchable, non-polymeric, widely used, low-cost, naturally rigid, metallic thin-film copper (Cu)-based flexible and non-invasive, spatially tunable, mobile thermal patch with wireless controllability, adaptability (tunes the amount of heat based on the temperature of the swollen portion), reusability, and affordability due to low-cost complementary metal oxide semiconductor (CMOS) compatible integration.

Wavy channel transistor for area efficient high performance operation

We report a wavy channel FinFET like transistor where the channel is wavy to increase its width without any area penalty and thereby increasing its drive current. Through simulation and experiments, we show the effectiveness of such device architecture is capable of high performance operation compared to conventional FinFETs with comparatively higher area efficiency and lower chip latency as well as lower power consumption.

High performance high-κ/metal gate complementary metal oxide semiconductor circuit element on flexible silicon

Thinned silicon based complementary metal oxide semiconductor (CMOS) electronics can be physically flexible. To overcome challenges of limited thinning and damaging of devices originated from back grinding process, we show sequential reactive ion etching of silicon with the assistance from soft polymeric materials to efficiently achieve thinned (40 μm) and flexible (1.5 cm bending radius) silicon based functional CMOS inverters with high-κ/metal gate transistors. Notable advances through this study shows large area of silicon thinning with pre-fabricated high performance elements with ultra-large-scale-integration density (using 90 nm node technology) and then dicing of such large and thinned (seemingly fragile) pieces into smaller pieces using excimer laser. The impact of various mechanical bending and bending cycles show undeterred high performance of flexible silicon CMOS inverters. Future work will include transfer of diced silicon chips to destination site, interconnects, and packaging to obtain full...

Zinc oxide integrated area efficient high output low power wavy channel thin film transistor

We report an atomic layer deposition based zinc oxide channel material integrated thin film transistor using wavy channel architecture allowing expansion of the transistor width in the vertical direction using the fin type features. The experimental devices show area efficiency, higher normalized output current, and relatively lower power consumption compared to the planar architecture. This performance gain is attributed to the increased device width and an enhanced applied electric field due to the architecture when compared to a back gated planar device with the same process conditions.

Deterministic Integration of Out-of-Plane Sensor Arrays for Flexible Electronic Applications.

A design strategy for fully flexible electrode arrays with out-of-plane through polymer vias (TPVs) for monolithic 3D integration of sensor readout circuitry is presented. The TPVs are formed using copper embedded in thin polyimide structure for support. The copper interconnects offer a stable impedance frequency response from DC to 100 kHz (Z ≈ 20 Ω, θ ≈ 0°).

Functional integrity of flexible n-channel metal–oxide–semiconductor field-effect transistors on a reversibly bistable platform

Flexibility can bring a new dimension to state-of-the-art electronics, such as rollable displays and integrated circuit systems being transformed into more powerful resources. Flexible electronics are typically hosted on polymeric substrates. Such substrates can be bent and rolled up, but cannot be independently fixed at the rigid perpendicular position necessary to realize rollable display-integrated gadgets and electronics. A reversibly bistable material can assume two stable states in a reversible way: flexibly rolled state and independently unbent state. Such materials are used in cycling and biking safety wristbands and a variety of ankle bracelets for orthopedic healthcare. They are often wrapped around an object with high impulsive force loading. Here, we study the effects of cumulative impulsive force loading on thinned (25 μm) flexible silicon-based n-channel metal–oxide–semiconductor field-effect transistor devices housed on a reversibly bistable flexible platform. We found that the transistors ...