Stretchable electronic systems built on soft substrates offer more conformal surface coverage and better durability than flexible electronics, and have generated significant research interests recently for potential applications in wearable/implantable health monitoring and diagnostic devices, electronic skin for prosthesis or soft robotics, stretchable displays and many more. Nevertheless, the large-area and low-cost fabrication of high-performance intrinsically stretchable electronic devices has remained to be extremely challenging. In this talk, I will present our recent work on addressing the two major challenges faced by stretchable electronics - the development of intrinsically-stretchable electronic materials and the need for scalable fabrication processes. We have developed nanomaterials-based metal, semiconductor, and dielectric materials with superior electronic property, stretchability, and inter-layer adhesion. Such materials are formulated as electronic inks to allow highly uniform and scalable material patterning using a inkjet-printed process, allowing us to achieve intrinsically stretchable thin-film transistors (TFTs) and integrated logic circuits made entirely by printing on ultrathin elastic polydimethylsiloxane (PDMS) substrates. Electrical and mechanical characterizations reveal that the TFTs and logic circuits can withstand up to 100% tensile strain along either channel length or channel width directions for thousands of cycles while showing no noticeable degradation in electrical performance. In addition to the above, I will also present our work on printed stretchable sensors and displays for wearable electronics and soft robotics applications. Our platform may offer a new entry into more sophisticated stretchable electronic systems with monolithically integrated sensors, actuators, and displays, fabricated by scalable and low-cost methods for real-life applications.
With the popularization of electronic devices and the demand for portability, low-power consumption has become crucial for integrated circuit chips. Two-dimensional (2D) semiconductors offer significant potential in constructing low-power devices due to their ultrathin thickness, enabling fully depletion operation. However, fabricating these 2D low-power devices, such as negative-capacitance transistors or tunneling transistors, often requires multiple layers of gate dielectrics or channel band engineering, adding complexity to the manufacturing process and posing challenges for their integration with silicon technology. In this work, we have developed low-power MoS2 metal–semiconductor field effect transistors utilizing a standard metal–semiconductor contact, which eliminates the need for gate dielectrics and semiconductor heterojunctions. It demonstrates a sharp subthreshold slope (SS ∼ 64 mV/dec), a minimum operating gate voltage range (−0.5 ∼ 1 V), a minimum current hysteresis (3.69 mV), and a stable threshold voltage close to 0 V (Vth ∼ −0.27 V). Moreover, we implemented an inverter circuit with a high voltage gain of 47.
The multifunctional integrated on-chip near-infrared (NIR) light source and detection devices based on vdW layered materials are increasingly sought after due to their broad applications, including optoelectronic communication, computing, and sensing. Most of luminescence or detection devices based on vdW layered materials are demonstrated to have only a single function due to the limitation of material properties. Here, we demonstrated a multifunctional integrated on-chip NIR electroluminescence (EL) and self-powered photodetector (SPPD) device constructed by stacking few-layer graphene (Gr) and layered γ-InSe to form asymmetric Gr/γ-InSe/Gr heterostructure. Room temperature electrically driven NIR from γ-InSe was successfully achieved by the high quality Schottky junction (rectification ratio up to "5×" 〖"10" 〗^"3" ), with a turn-on voltage of ~ 1.4 V. The γ-InSe EL maintained over 90 % initial EL intensity after two hours continuous operation in air. Meanwhile, the Gr/γ-InSe/Gr SPPD exhibits a broad spectrum photoresponse (405-940nm), low specific noise current (8.7"×" 10-26 A2/Hz), high specific detectivity (~ 108 Jones @ 405 nm) and high-quality reflective imaging. Our results establish a simple preparation and tunable vdW layered material multifunctional integrated NIR EL and SPPD device, indicating the promise of γ-InSe for on-chip integrated optoelectronic devices.
Abstract Neuromorphic hardware based on artificial synaptic devices has great potential to break the bottleneck of von Neumann architecture, which makes it possible to emulate the working mode of the human brain with low power consumption and high operation efficiency. However, current synaptic devices can barely detect photons and are bio‐incompatible for future all‐in‐one visual perception technology. Here, synaptic photoconductors based on an organic–inorganic hybrid structure, and composed of photosensitive bacteriorhodopsin protein layer and zinc oxide film are reported. The synaptic photoconductors demonstrate tunable synaptic plasticity with the modulation of the light illumination time and power intensity. The working mechanism of the photogating effect induced by the proton pump process of bR protein molecules is further investigated in detail. Assisting with these properties, the imaging memorization and preprocessing function are successfully emulated by the synaptic photoconductors. The prototype photosynaptic devices provide a unique opportunity to realize artificial synapses, enabling neuromorphic hardware.
Two-dimensional (2D) infrared photodetectors always suffer from low quantum efficiency (QE) because of the limited atomically thin absorption. Here, we reported 2D black phosphorus (BP)/Bi2O2Se van der Waals (vdW) photodetectors with momentum-matching and band-alignment heterostructures to achieve high QE. The QE was largely improved by optimizing the generation, suppressing the recombination, and improving the collection of photocarriers. Note that momentum-matching BP/Bi2O2Se heterostructures in k-space lead to the highly efficient generation and transition of photocarriers. The recombination process can be largely suppressed by lattice mismatching-immune vdW interfaces. Furthermore, type II BP/Bi2O2Se vdW heterostructures could also assist fast transport and collection of photocarriers. By constructing momentum-matching and band-alignment heterostructures, a record-high QE of 84% at 1.3 micrometers and 76.5% at 2 micrometers have been achieved in BP/Bi2O2Se vdW photodetectors.
Abstract A unique direct printing method is developed to additively pattern silver nanowires (AgNWs) with length of up to ≈40 µm. Uniform and well‐defined AgNW features are printed on various substrates by optimizing a series of parameters including ink composition, printing speed, nozzle size, substrate temperature, and hydrophobicity of the substrate surface. The capability of directly printing such long AgNWs is essential for stretchable electronics applications where mechanical compliance is required as manifested by a systematic study comparing the electrical and electromechanical performance of printed AgNW features with different nanowire lengths. Such printed AgNWs are used to demonstrate biaxially stretchable conductors, ultrasensitive capacitive pressure sensor arrays, and stretchable electroluminescent displays, indicating their great potential for applications in low‐cost wearable electronics. This strategy is adaptable to other material platforms like semiconducting nanowires, which may offer a cost‐effective entry to various nanowire‐based mechanically compliant sensory and optoelectronic systems.
Photodetectors (PDs) are crucial in modern society, as they enable the detection of a diverse range of light-based signals. With the exponential increase in their development, materials are being used to create a wide range of PDs that play critical roles in enabling various applications and technologies. Image sensor technology has been hindered due to the lack of a universal system that can integrate all types of PDs with silicon-based readout integrated circuits (ROICs). To address this issue, we conducted experiments using two-dimensional materials as an example. We fabricated high-performance MoS2/MoTe2-based photodetectors and identified the most suitable ROICs to pair with them. This established a solid foundation for further research in the field of image sensors. We developed and implemented a versatile testing system that uses a printed circuit board to connect the PD and ROIC. After the ROIC generates the sampled signal, it is collected and processed by algorithms, which overcome device uniformity limitations and produce a high-quality image that is visible to the naked eye. This universal system can be used with a wide range of PD and ROIC types made from different materials, making it highly convenient for diverse testing applications and the development of diverse image sensor types. This robust new platform is expected to spur further innovation and advancements in this rapidly developing field.
Graphene is a promising candidate material for high-speed and ultra-broadband photodetectors. However, graphene-based photodetectors suffer from low photoreponsivity and Ilight/Idark ratios due to their negligible-gap nature and small optical absorption. Here, a new type of graphene/InAs nanowire (NW) vertically stacked heterojunction infrared photodetector is reported, with a large photoresponsivity of 0.5 AW−1 and Ilight/Idark ratio of 5 × 102, while the photoresponsivity and Ilight/Idark ratio of graphene infrared photodetectors are 0.1 mAW−1 and 1, respectively. The Fermi level (EF ) of graphene can be widely tuned by the gate voltage owing to its 2D nature. As a result, the back-gated bias can modulate the Schottky barrier (SB) height at the interface between graphene and InAs NWs. Simulations further demonstrate the rectification behavior of graphene/InAs NW heterojunctions and the tunable SB controls charge transport across the vertically stacked heterostructure. The results address key challenges for graphene-based infrared detectors, and are promising for the development of graphene electronic and optoelectronic applications.
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