Bulk Monocrystalline Silicon Research Articles

Fully spherical stretchable silicon photodiodes array for simultaneous 360 imaging

Imaging is one of the important wonders of today's world. While everyday millions of snaps are taken, new advances like panoramic imaging have become increasingly popular. However, as of today an imaging system which can simultaneously capture images from all 360° viewpoints with a single sensor has not been achieved. Here, we show a physically flexible and stretchable version of arrayed silicon photodiodes made from low-cost bulk monocrystalline silicon (100) that can capture simultaneous omnidirectional images. The present report, with multiple wavelength detection, fast photoresponsivity, a wide viewing angle, selective aberration, and dynamic focusing enabled by 3D printed pneumatic actuators (note, today millions of image sensors can be integrated in mm2 area), overcomes previous demonstrations of only hemispherical photodetection capability. Such imaging capability will make unmanned air vehicles or self-driven cars safer, affordable augmented and virtual reality and more importantly, in-vivo biomedical imaging will be more effective.

Expandable Polymer Enabled Wirelessly Destructible High‐Performance Solid State Electronics

In today's digital age, the increasing dependence on information also makes us vulnerable to potential invasion of privacy and cyber security. Consider a scenario in which a hard drive is stolen, lost, or misplaced, which contains secured and valuable information. In such a case, it is important to have the ability to remotely destroy the sensitive part of the device (e.g., memory or processor) if it is not possible to regain it. Many emerging materials and even some traditional materials like silicon, aluminum, zinc oxide, tungsten, and magnesium, which are often used for logic processor and memory, show promise to be gradually dissolved upon exposure of various liquid medium. However, often these wet processes are too slow, fully destructive, and require assistance from the liquid materials and their suitable availability at the time of need. This study shows Joule heating effect induced thermal expansion and stress gradient between thermally expandable advanced polymeric material and flexible bulk monocrystalline silicon (100) to destroy high‐performance solid state electronics as needed and under 10 s. This study also shows different stimuli‐assisted smartphone‐operated remote destructions of such complementary metal oxide semiconductor electronics.

Stretchable and foldable silicon-based electronics

Flexible and stretchable semiconducting substrates provide the foundation for novel electronic applications. Usually, ultra-thin, flexible but often fragile substrates are used in such applications. Here, we describe flexible, stretchable, and foldable 500-μm-thick bulk mono-crystalline silicon (100) “islands” that are interconnected via extremely compliant 30-μm-thick connectors made of silicon. The thick mono-crystalline segments create a stand-alone silicon array that is capable of bending to a radius of 130 μm. The bending radius of the array does not depend on the overall substrate thickness because the ultra-flexible silicon connectors are patterned. We use fracture propagation to release the islands. Because they allow for three-dimensional monolithic stacking of integrated circuits or other electronics without any through-silicon vias, our mono-crystalline islands can be used as a “more-than-Moore” strategy and to develop wearable electronics that are sufficiently robust to be compatible with flip-chip bonding.

Enhanced cooling in mono-crystalline ultra-thin silicon by embedded micro-air channels

In today’s digital world, complementary metal oxide semiconductor (CMOS) technology enabled scaling of bulk mono-crystalline silicon (100) based electronics has resulted in their higher performance but with increased dynamic and off-state power consumption. Such trade-off has caused excessive heat generation which eventually drains the charge of battery in portable devices. The traditional solution utilizing off-chip fans and heat sinks used for heat management make the whole system bulky and less mobile. Here we show, an enhanced cooling phenomenon in ultra-thin (>10 μm) mono-crystalline (100) silicon (detached from bulk substrate) by utilizing deterministic pattern of porous network of vertical “through silicon” micro-air channels that offer remarkable heat and weight management for ultra-mobile electronics, in a cost effective way with 20× reduction in substrate weight and a 12% lower maximum temperature at sustained loads. We also show the effectiveness of this event in functional MOS field effect transistors (MOSFETs) with high-κ/metal gate stacks.

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 today's 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.

Study of harsh environment operation of flexible ferroelectric memory integrated with PZT and silicon fabric

Flexible memory can enable industrial, automobile, space, and smart grid centered harsh/extreme environment focused electronics application(s) for enhanced operation, safety, and monitoring where bent or complex shaped infrastructures are common and state-of-the-art rigid electronics cannot be deployed. Therefore, we report on the physical-mechanical-electrical characteristics of a flexible ferroelectric memory based on lead zirconium titanate as a key memory material and flexible version of bulk mono-crystalline silicon (100). The experimented devices show a bending radius down to 1.25 cm corresponding to 0.16% nominal strain (high pressure of ∼260 MPa), and full functionality up to 225 °C high temperature in ambient gas composition (21% oxygen and 55% relative humidity). The devices showed unaltered data retention and fatigue properties under harsh conditions, still the reduced memory window (20% difference between switching and non-switching currents at 225 °C) requires sensitive sense circuitry for proper functionality and is the limiting factor preventing operation at higher temperatures.

Flexible–Stretchable Micro Lithium Ion Batteries for Implantable, Wearable and Embedded Electronics

Future generation electronics which will be in the form of implantable, wearable and/or embedded format will require reliable power supply. Remote wireless charging or grid power supplied battery or energy harvesting – in any form of power supply, energy storage or battery will play critical role. In that regard, coin cell batteries and/or super capacitors are not suitable due to their bulky profile and toxic materials involved in their manufacturing. From that perspective, rechargeable micro lithium ion batteries (mLIB) are promising option for such energy storage. They offer high operating voltage, long life and high energy capacity. However, one major challenge is to achieve flexible and stretchable battery which is critical physical form for implantable, wearable and/or embedded electronics. In recent years, two routes have been pursued for such flexible mLIB fabrication: (1) exploration of new types of inherently compliant materials for battery electrodes such as carbon nanotube, graphene, carbon grease and slurry mixes of nanomaterials and (2) thinned inorganic thin film based battery. Although nano-scale thin films based mLIBs are reliable from their manufacturing and performance perspective, they are fabricated on rigid substrates. One option is to use exfoliation of a mica substrate to release battery stack – however, mica substrates are unconventional and physical delamination of such substrate is a low throughput/low yield process. In this work we present a soft etch back based flexible mLIB formation process. First we fabricate the battery on bulk mono-crystalline silicon (100) using lithium based thin films including cobalt, phosphorous alloy and then we spin a soft material on top of it. Next we flip the whole system and etch back the silicon using reactive ion etching in sequential manner. Next we spin another soft material on the flipped “chip”. Finally, we remove the first soft material selectively over the thin films present and the second soft material. In this way, we obtain 40 mm thick silicon based mLIB with an enhanced normalized capacity of 146 mAh/cm2 even after 120 cycles of continued operation. Comparison with a traditional rigid battery (fabricated in batch with the flexible one) shows comparable to superior performance.

Electrical Analysis of High Dielectric Constant Insulator and Metal Gate Metal Oxide Semiconductor Capacitors on Flexible Bulk Mono-Crystalline Silicon

We report on the electrical study of high dielectric constant insulator and metal gate metal oxide semiconductor capacitors (MOSCAPs) on a flexible ultra-thin $(25~\mu{\rm m})$ silicon fabric which is peeled off using a CMOS compatible process from a standard bulk mono-crystalline silicon substrate. A lifetime projection is extracted using statistical analysis of the ramping voltage $({\rm V}_{\rm ramp})$ breakdown and time dependent dielectric breakdown data. The obtained flexible MOSCAPs operational voltages satisfying the 10 years lifetime benchmark are compared to those of the control MOSCAPs, which are not peeled off from the silicon wafer.

Towards neuromorphic electronics: Memristors on foldable silicon fabric

The advantages associated with neuromorphic computation are rich areas of complex research. We address the fabrication challenge of building neuromorphic devices on structurally foldable platform with high integration density. We present a CMOS compatible fabrication process to demonstrate for the first time memristive devices fabricated on bulk monocrystalline silicon (100) which is next transformed into a flexible thin sheet of silicon fabric with all the pre-fabricated devices. This process preserves the ultra-high integration density advantage unachievable on other flexible substrates. In addition, the memristive devices are of the size of a motor neuron and the flexible/folded architectural form factor is critical to match brain cortex׳s folded pattern for ultra-compact design.

Transformational Silicon Electronics

In today's 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 industry's 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)

Flexible and semi-transparent high performance thermoelectric energy harvesters are fabricated on low cost bulk mono-crystalline silicon (100) wafers. The released silicon is only 3.6% as thick as bulk silicon reducing the thermal loss significantly and generating nearly 30% more output power than unpeeled harvesters. This generic batch processing is a pragmatic way of transforming traditional silicon circuitry for extremely deformable high-performance integrated electronics.

Stimulated terahertz emission from group-V donors in silicon under intracenter photoexcitation

Frequency-tunable radiation from the free electron laser FELIX was used to excite neutral phosphorus and bismuth donors embedded in bulk monocrystalline silicon. Lasing at terahertz frequencies has been observed at liquid helium temperature while resonant pumping of odd parity impurity states. The threshold was about two orders of magnitude below the value for photoionization pumping. The influence of nonequilibrium intervalley TO phonons on the population of excited Bi impurity states is discussed.

Terahertz emission from silicon doped by shallow impurities

A new approach to generate stimulated emission in the terahertz (THz) range of the electromagnetic spectrum is presented. At low temperatures, population inversion between excited states of shallow impurity centers in silicon can occur due to peculiarities of electron–phonon interaction. The terahertz stimulated emission from impurity transitions was observed from bulk monocrystalline silicon doped by group V elements (P, Bi), excited by CO 2 laser radiation.