Galo A. Torres Sevilla

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.

Can We Build a Truly High Performance Computer Which is Flexible and Transparent

State-of-the art computers need high performance transistors, which consume ultra-low power resulting in longer battery lifetime. Billions of transistors are integrated neatly using matured silicon fabrication process to maintain the performance per cost advantage. In that context, low-cost mono-crystalline bulk silicon (100) based high performance transistors are considered as the heart of todays computers. One limitation is silicons rigidity and brittleness. Here we show a generic batch process to convert high performance silicon electronics into flexible and semi-transparent one while retaining its performance, process compatibility, integration density and cost. We demonstrate high-k/metal gate stack based p-type metal oxide semiconductor field effect transistors on 4 inch silicon fabric released from bulk silicon (100) wafers with sub-threshold swing of 80 mV dec−1 and on/off ratio of near 104 within 10% device uniformity with a minimum bending radius of 5 mm and an average transmittance of ~7% in the visible spectrum.

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

Structural and electrical characteristics of high-k/metal gate metal oxide semiconductor capacitors fabricated on flexible, semi-transparent silicon (100) fabric

In pursuit of flexible computers with high performance devices, we demonstrate a generic process to fabricate 10 000 metal-oxide-semiconductor capacitors (MOSCAPs) with semiconductor industrys most advanced high-k/metal gate stacks on widely used, inexpensive bulk silicon (100) wafers and then using a combination of iso-/anisotropic etching to release the top portion of the silicon with the already fabricated devices as a mechanically flexible (bending curvature of 133 m−1), optically semi-transparent silicon fabric (1.5 cm × 3 cm × 25 μm). The electrical characteristics show 3.7 nm effective oxide thickness, −0.2 V flat band voltage, and no hysteresis from the fabricated MOSCAPs.

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.

Nonplanar Nanoscale Fin Field Effect Transistors on Textile, Paper, Wood, Stone, and Vinyl via Soft Material-Enabled Double-Transfer Printing.

The ability to incorporate rigid but high-performance nanoscale nonplanar complementary metal-oxide semiconductor (CMOS) electronics with curvilinear, irregular, or asymmetric shapes and surfaces is an arduous but timely challenge in enabling the production of wearable electronics with an in situ information-processing ability in the digital world. Therefore, we are demonstrating a soft-material enabled double-transfer-based process to integrate flexible, silicon-based, nanoscale, nonplanar, fin-shaped field effect transistors (FinFETs) and planar metal-oxide-semiconductor field effect transistors (MOSFETs) on various asymmetric surfaces to study their compatibility and enhanced applicability in various emerging fields. FinFET devices feature sub-20 nm dimensions and state-of-the-art, high-κ/metal gate stacks, showing no performance alteration after the transfer process. A further analysis of the transferred MOSFET devices, featuring 1 μm gate length, exhibits an ION value of nearly 70 μA/μm (VDS = 2 V, VGS = 2 V) and a low subthreshold swing of around 90 mV/dec, proving that a soft interfacial material can act both as a strong adhesion/interposing layer between devices and final substrate as well as a means to reduce strain, which ultimately helps maintain the devices performance with insignificant deterioration even at a high bending state.

Room to High Temperature Measurements of Flexible SOI FinFETs With Sub-20-nm Fins

We report the temperature dependence of the core electrical parameters and transport characteristics of a flexible version of fin field-effect transistor (FinFET) on silicon-on-insulator (SOI) with sub-20-nm wide fins and high-k/metal gate-stacks. For the first time, we characterize them from room to high temperature (150 °C) to show the impact of temperature variation on drain current, gate leakage current, and transconductance. Variation of extracted parameters, such as low-field mobility, subthreshold swing, threshold voltage, and ON-OFF current characteristics, is reported too. Direct comparison is made to a rigid version of the SOI FinFETs. The mobility degradation with temperature is mainly caused by phonon scattering mechanism. The overall excellent devices performance at high temperature after release is outlined proving the suitability of truly high-performance flexible inorganic electronics with such advanced architecture.

Printed Organic and Inorganic Electronics: Devices To Systems

Affordable and versatile printed electronics can play a critical role for large area applications, such as for displays, sensors, energy harvesting, and storage. Significant advances including commercialization in the general area of printed electronics have been based on organic molecular electronics. Still some fundamental challenges remain: thermal instability, modest charge transport characteristics, and limited lithographic resolution. In the last decade, one-dimensional nanotubes and nanowires, like carbon nanotubes and silicon nanowires, followed by two-dimensional materials, like graphene and transitional dichalcogenide materials, have shown interesting promise as next-generation printed electronic materials. Challenges, such as non-uniformity in growth, limited scalability, and integration issues, need to be resolved for the viable application of these materials to technology. Recently, the concept of printed high-performance complementary metal–oxide semiconductor electronics has also emerged and been proven successful for application to electronics. Here, we review progress in CMOS technology and applications, including challenges faced and opportunities revealed.

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 ...