Single Crystalline Silicon Nanomembranes Research Articles

A smart coating with integrated physical antimicrobial and strain-mapping functionalities for orthopedic implants.

The prevalence of orthopedic implants is increasing with an aging population. These patients are vulnerable to risks from periprosthetic infections and instrument failures. Here, we present a dual-functional smart polymer foil coating compatible with commercial orthopedic implants to address both septic and aseptic failures. Its outer surface features optimum bioinspired mechano-bactericidal nanostructures, capable of killing a wide spectrum of attached pathogens through a physical process to reduce the risk of bacterial infection, without directly releasing any chemicals or harming mammalian cells. On its inner surface in contact with the implant, an array of strain gauges with multiplexing transistors, built on single-crystalline silicon nanomembranes, is incorporated to map the strain experienced by the implant with high sensitivity and spatial resolution, providing information about bone-implant biomechanics for early diagnosis to minimize the probability of catastrophic instrument failures. Their multimodal functionalities, performance, biocompatibility, and stability are authenticated in sheep posterolateral fusion model and rodent implant infection model.

Flexible Hybrid Single-Crystalline Silicon Nanomembrane Thin-Film Transistor with Organic Polymeric Polystyrene as a Gate Dielectric on a Plastic Substrate

Flexible thin-film transistors (TFTs) play an important role in flexible integrated circuits (ICs). Hybrid integrated transistors are highly desirable because of their high performance and simplified process. However, TFTs with a hybrid integrated heterostructure of single-crystalline semiconductor/organic dielectric layers have not yet been discussed. In this work, a flexible hybrid TFT comprised of a single-crystalline silicon nanomembrane (SiNM) semiconductor and polystyrene (PS) gate dielectric was fabricated on a PET substrate. The surface morphology of the PS dielectric layer on the PET substrate was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The electrical characteristics of the dielectric layer (PS) were also analyzed. SiNM was processed with a complementary metal–oxide–semiconductor (CMOS)-compatible process and subsequently transferred to the PET substrate with a PS/ITO stacked layer to complete the assembly of the flexible hybrid SiNM/PS TFT. The electrical properties of the flexible hybrid TFT were characterized under different bending conditions (i.e., flat and bending radii of 21, 38.5, and 77.5 mm). Furthermore, the stress analysis of TFTs influenced by a variation of the dielectric materials (i.e., PS, SiO2, and Al2O3), the adhesion conditions of the SiNM/PS interface, and the dielectric thickness were also discussed. The results revealed the potential of combining an organic polymeric dielectric with inorganic single-crystalline nanomembranes to fabricate high-performance flexible hybrid TFTs.

Single-crystalline silicon nanomembrane thin-film transistors with anodized aluminum oxide as a gate dielectric on rigid and flexible substrates

Flexible integrated circuits have gained a lot of attention in recent years for their emerging applications in wearable electronics. Flexible thin-film transistors (TFTs) with low-costs and high-performance are highly desirable as essential and fundamental elements for most flexible applications. In this paper, we fabricate single-crystalline silicon nanomembrane (SiNM)-based TFTs with anodized aluminum oxide (AAO) as a dielectric material on glass and flexible plastic substrates. Good quality AAO was obtained on plastic substrates at room temperature. Atomic force microscopy (AFM)was used for the surface morphology of the AAO gate dielectric layers on different substrates (i.e. glass, polyethylene terephthalate (PET), and SU-8 coated PET). The electrical characteristics of the AAO gate dielectric layers on different substrates were also analyzed with metal–insulator–metal capacitors. The SiNMs were processed with a complementary metal oxide semiconductor (CMOS) compatible semiconductor process (e.g. photolithography, ion implantation, thermal annealing, reactive ion etching, metal evaporation, etc), and then transferred to the substrates with AAO/aluminum stack layers. The performance of the transistors on glass and plastic substrates was characterized. Compared with the TFT fabricated on a glass substrate, the TFT fabricated directly on a PET substrate had lower performance due to poor surface roughness. For optimization of the surface roughness, the PET was modified with a coating of SU-8 photoresist. In this way, the TFT had properties close to that on a glass substrate. AAO that can be manufactured at room temperature provides a simple and low-cost solution for high-performance flexible single-crystalline SiNM TFTs.

(Invited) Silicon Nanomembrane-Based Flexible Photodetector and Sensors

Nanomembranes, as a new type of nanomaterials with a thickness below hundreds of nanometers, offer great opportunities for practical applications in the Internet of Things era.[1] The reduction of material thickness creates possibilities for brittle inorganic semiconductors to become flexible, which is essential for the realization of bendable and stretchable electronics.[2-4] As one of the important application forms of flexible electronics, the bendable photodetector is an essential part as the sensing component for a most integrated system.[5,6] Flexible photodetectors based on single-crystalline silicon nanomembranes (Si-NMs) have attracted great attention due to their excellent mechanical bendability, optoelectronic sensitivity, and response seed and integrability to conventional CMOS chips.[7-10] We report a high-performance Si-NM phototransistor through a wafer-compatible process.[11] This process reverses all electrodes to the backside of the final Si-NM phototransistor and permits complete exposure of the light-sensitive channel to illumination. The phototransistor fabricated via this approach exhibits an ultra-high photo-to-dark current ratio of ~106 (Figure 1(a)) as well as excellent characters such as good linearity output, high gains, fast response speed, and tunable spectrum responsibility. We further demonstrate that the device can be used as an expandable working platform for different stimulations. Figure 1(b) exhibits the optical images of the fabricated devices. Figure 1(c) schematically illustrated the functionality of this system in the optoelectronic detecting of specific molecules. This functionality can be realized by decorating the top surface of phototransistor with certain sensitive materials (e.g. gas chromic materials). The function expandability of the flexible Si-NM-based device as well as the wafer-compatible fabrication exhibit great potential for the sensing functions in the future portable/wearable electronic integrating system with multifunctional applications. Acknowledgment: This work is supported by the Natural Science Foundation of China (51711540298, U1632115, 51602056), Science and Technology Commission of Shanghai Municipality (17JC1401700), the National Key Technologies R&D Program of China (2015ZX02102-003) and the Changjiang Young Scholars Program of China. Part of the experimental work has been carried out in Fudan Nanofabrication Laboratory.

Dielectric ceramics/TiO2/single-crystalline silicon nanomembrane heterostructure for high performance flexible thin-film transistors on plastic substrates.

A dielectric ceramics/TiO2/single-crystalline silicon nanomembrane (SiNM) heterostructure is designed and fabricated for high performance flexible thin-film transistors (TFTs). Both the dielectric ceramics (Nb2O3–Bi2O3–MgO) and TiO2 are deposited by radio frequency (RF) magnetron sputtering at room temperature, which is compatible with flexible plastic substrates. And the single-crystalline SiNM is transferred and attached to the dielectric ceramics/TiO2 layers to form the heterostructure. The experimental results demonstrate that the room temperature processed heterostructure has high quality because: (1) the Nb2O3–Bi2O3–MgO/TiO2 heterostructure has a high dielectric constant (∼76.6) and low leakage current. (2) The TiO2/single-crystalline SiNM structure has a relatively low interface trap density. (3) The band gap of the Nb2O3–Bi2O3–MgO/TiO2 heterostructure is wider than TiO2, which increases the conduction band offset between Si and TiO2, lowering the leakage current. Flexible TFTs have been fabricated with the Nb2O3–Bi2O3–MgO/TiO2/SiNM heterostructure on plastic substrates and show a current on/off ratio over 104, threshold voltage of ∼1.2 V, subthreshold swing (SS) as low as ∼0.2 V dec−1, and interface trap density of ∼1012 eV−1 cm−2. The results indicate that the dielectric ceramics/TiO2/SiNM heterostructure has great potential for high performance TFTs.

Dissolution Chemistry and Biocompatibility of Single-Crystalline Silicon Nanomembranes and Associated Materials for Transient Electronics

Single-crystalline silicon nanomembranes (Si NMs) represent a critically important class of material for high-performance forms of electronics that are capable of complete, controlled dissolution when immersed in water and/or biofluids, sometimes referred to as a type of "transient" electronics. The results reported here include the kinetics of hydrolysis of Si NMs in biofluids and various aqueous solutions through a range of relevant pH values, ionic concentrations and temperatures, and dependence on dopant types and concentrations. In vitro and in vivo investigations of Si NMs and other transient electronic materials demonstrate biocompatibility and bioresorption, thereby suggesting potential for envisioned applications in active, biodegradable electronic implants.

On-chip intra- and inter-layer grating couplers for three-dimensional integration of silicon photonics

We present on-chip intra- and inter-layer grating couplers fabricated on double-layer, single crystalline silicon nanomembranes. The silicon nanomembranes were fabricated using an adhesive bonding process. The grating couplers are based on subwavelength nanostructures operating at the transverse-electric polarization. Such nanostructures can be patterned in a single lithography/etching process. Simultaneous intra-layer coupling to separate silicon photonic layers is demonstrated through grating couplers with peak efficiencies of 18% and 44% per grating coupler for bottom and top layer, respectively, at 1550 nm wavelength. The inter-layer grating coupler has an efficiency of 25% at 1560 nm wavelength with a 3 dB bandwidth of 41 nm.

A Multifunction Heterojunction Formed Between Pentacene and a Single‐Crystal Silicon Nanomembrane

AbstractA mesh patterned n‐type single‐crystalline silicon nanomembrane (SiNM) created from a silicon‐on‐insulator (SOI) wafer is complementally combined with a p‐type pentacene layer to form a heterogeneous p‐n junction on a flexible plastic substrate. Excellent rectifying characteristics are obtained from the heterogeneous p‐n diode. The diode also exhibits photosensitivity at visible wavelengths with a photo‐to‐dark current ratio exceeding four orders, a responsivity of 0.7 A/W, and an external quantum efficiency of 21.9% at 633 nm. Over 60% average transmittance in the visible spectrum is measured from the heterogeneous multilayer junction on a plastic substrate. Outstanding mechanical bending characteristics are observed with up to 1.08% of strain applied to the diode. These results suggest that organic‐inorganic heterogeneous integration may be a viable strategy to build flexible organic‐inorganic heterojunction devices and thus enable a number of novel multifunctional applications.

Impact of strain on radio frequency characteristics of flexible microwave single-crystalline silicon nanomembrane p-intrinsic-n diodes on plastic substrates

This letter presents radio frequency (rf) characterization of flexible microwave single-crystalline silicon nanomembrane (SiNM) p-intrinsic-n (PIN) diodes on plastic substrate under various uniaxial mechanical tensile bending strains. The flexible single-crystalline SiNM PIN diode shows significant/negligible performance enhancement on strains under forward/reverse operation modes from dc to 20 GHz. An rf strain equivalent circuit model is developed to analyze the underlying mechanism and reveals unproportional device parameters change with bending strains (∼0.4% tensile strain induces ∼10% change for diode internal and parasitic inductance/resistance). The study provides guidelines of properly designing and using single-crystalline SiNMs diodes for flexible monolithic microwave integrated circuits.

RF model of flexible microwave single-crystalline silicon nanomembrane PIN diodes on plastic substrate

This paper reports the realization and RF modeling of flexible microwave P-type-Intrinsic-N-type (PIN) diodes using transferrable single-crystalline Si nanomembranes (SiNMs) that are monolithically integrated on low-cost, flexible plastic substrates. With high-energy, high-dose ion implantation and high-temperature annealing before nanomembrane release and transfer process, the parasitic parameters (i.e. resistance, inductance, etc.) are effectively reduced, and the flexible PIN diodes achieve good high-frequency response. With consideration of the flexible device fabrication, structure and layout configuration, a RF model of the microwave single-crystalline Si nanomembrane PIN diodes on plastic substrate is presented. The RF/microwave equivalent circuit model achieves good agreement with the experimental results of the single-crystalline SiNM PIN diodes with different diode areas, and reveals the most influential factors to flexible diode characteristics. The study provides guidelines for properly designing and using single-crystalline SiNMs for flexible RF/microwave diodes and demonstrates the great possibility of flexible monolithic microwave integrated systems.

Colloidal quantum dot absorption enhancement in flexible Fano filters

We report here modified absorption property of colloidal quantum dots (CQDs) inside flexible Fano filters—made of patterned single crystalline silicon nanomembrane transferred onto flexible plastic substrates. Enhanced optical absorption was obtained both experimentally and theoretically, when the CQD absorption peak spectrally overlaps with Fano resonance peak. On the other hand, suppressed absorption was observed when the Fano resonance has no spectral overlap with the CQD absorption bands.

Study of 2-D photon crystal Fano slab filters for biological sensing

A new compact optical Fano filter suitable for biological sensing is proposed, which patterns photon crystal in single crystalline silicon nanomembranes (SiNMs) and transferring onto transparent glass substrates. The effects of air hole size and silicon thickness on the transmission characteristics of new filter are numerically investigated by using three-dimensional finite-difference time-domain (FDTD) technique, the spectral response is also studied by back-filling bio-liquid. The results show that the dip wavelength will shift toward longer wavelength by either reducing air hole radius or filling bioliquid. The number of dips will increase with the increase of silicon thickness. The size of proposed filter can be less than 1 mm2.

Bend, Buckle, and Fold: Mechanical Engineering with Nanomembranes

Research on nanomembranes and graphene sheets represents the "third wave" of work on nanomaterials, following earlier studies of nanoparticles/fullerenes and, somewhat later, nanowires/nanotubes. Inorganic semiconductor nanomembranes are particularly appealing due to their materials diversity, the ease with which they can be grown with high quality over large areas, and the ability to exploit them in unique, high-performance electronic and optoelectronic systems. The mechanics of such nanomembranes and the coupling of strain to their electronic properties are topics of considerable current interest. A new paper by the Lagally group in this issue combines single-crystalline silicon nanomembranes with chemical vapor deposition techniques to form "mechano-electronic" superlattices whose properties could lead to unusual classes of electronic devices.

Fano filters based on transferred silicon nanomembranes on plastic substrates

We report here the characteristics of surface-normal optical filters based on Fano resonances on patterned single crystalline silicon nanomembranes (SiNMs), which were fabricated and transferred onto transparent plastic substrates using a SiNM wet transfer process. Detailed experimental and theoretical analyses were carried out on the angular- and polarization-dependent transmission properties. The filter transmission is independent of the incident beam polarization under surface-normal conditions. Angle-independent transmission was observed for specific Fano resonances with certain polarizations. The measured angle-dependent transmission agrees well with the simulated transmission and dispersion properties based on the propagation wave-vector analysis.

Surface-normal Fano filters based on transferred silicon nanomembranes on glass substrates

Surface-normal optical filters are reported based on Fano resonances in patterned single crystalline silicon nanomembranes (SiNM), which were fabricated and transferred onto transparent glass substrates using a disruptive wet transfer process. The measured filter transmission results agree well with the design using a three-dimensional finite-difference time-domain technique. Using the SiNM wet transfer and stacking process, vertically stacked ultra-compact surface normal filters, switches, modulators and spectrally-selective photodetectors will become feasible.