Phototransistor Array Research Articles

Wafer-scale high-performance organic phototransistor arrays

Wafer-scale high-performance organic phototransistor arrays

Opto-electronic responses of large area WSe2 layers synthesized by chemical conversion of WO3 thin films

Atomically thin tungsten diselenide (WSe2) has drawn much interest due to its remarkable optical properties and potential applications in next-generation optoelectronics and energy harvesting devices. High-quality, wafer-scale synthesis of such two-dimensional (2D) semiconductors is necessary for their practical applications. Chemical vapor deposition (CVD) is a promising method for synthesizing large-area thin films of 2D materials where the constituent elements are of widely different vapor pressure. Herein, we demonstrate large-area synthesis of the 2H phase of WSe2 with a precise control over the 2D film thickness. The first step of this process is the deposition of tungsten trioxide (WO3) films of a well-defined thickness by thermal evaporation over large areas. The subsequent selenization of these films in an atmospheric pressure CVD reactor, yields high-quality uniform films of WSe2. The quality of these films is ascertained by measuring their characteristic Raman active vibrational modes and layer thickness dependent optical absorption and photoluminescence. The photoconductivity (PC) of these films has been measured with 405, 532 and 915 nm laser excitation. We note an increase in the PC of the films with their thickness. The best photoresponsivity and detectivity obtained are 11.3 mA/W and 1.42 × 108 Jones respectively. These results are promising to create photo-transistor arrays over large areas using such WO3 processed films.

Rotation-invariant image recognition using interconnected floating-gate phototransistor

Rotational invariance is fundamental for robust image recognition systems, ensuring accurate analysis irrespective of image orientation. However, existing systems predominantly reliant on software often encounter challenges such as increased computational demands and compromises between processing speed and accuracy. In this study, we propose leveraging the interconnected floating-gate (FG) structure as an effective hardware-level solution to achieve rotational invariance in image recognition. Our design features a reconfigurable two-dimensional material FG phototransistor array, where each processing unit integrates four sensory devices sharing a common FG. This configuration facilitates uniform distribution of stored charges across the interconnected FG layer, which is typically made of metal, enabling consistent application of a single weight matrix to images across varied rotational conditions. The photoactive material, tungsten diselenide (WSe2), possesses a distinctive bipolar property that facilitates both hole and electron tunneling into the FG layer. This property directly contributes to the efficiency of state transition within the setup and improves its overall adaptability. In this manner, our design achieves stable and predictable outputs in recognizing identical digital numbers regardless of their rotation, while also demonstrating variable performance essential for accurately distinguishing between different digital numbers. This dual capability guarantees both the adaptability and precision required for rotation-invariant image recognition, suggesting that our work may open up a promising venue for exploring advanced hardware designs, such as optimized interconnected FG architectures, tailored for enhancing recognition accuracy and efficiency in the field of intelligent visual systems.

Flexible Phototransistor Array Enhanced by Coupling the Piezo‐Phototronic Effect and the Flexoelectric Effect for Strain/Optical Sensing and Imaging

Flexible Phototransistor Array Enhanced by Coupling the Piezo‐Phototronic Effect and the Flexoelectric Effect for Strain/Optical Sensing and Imaging

An Active-Matrix Synaptic Phototransistor Array for In-Sensor Spectral Processing.

The human retina perceives and preprocesses the spectral information of incident light, enabling fast image recognition and efficient chromatic adaptation. In comparison, it is reluctant to implement parallel spectral preprocessing and temporal information fusion in current complementary metal-oxide-semiconductor (CMOS) image sensors, requiring intricate circuitry, frequent data transmission, and color filters. Herein, an active-matrix synaptic phototransistor array (AMSPA) is developed based on organic/inorganic semiconductor heterostructures. The AMSPA provides wavelength-dependent, bidirectional photoresponses, enabling dynamic imaging and in-sensor spectral preprocessing functions. Specifically, near-infrared light induces inhibitory photoresponse while UV light results in exhibitory photoresponse. With rational structural design of the organic/inorganic hybrid heterostructures, the current dynamic range of phototransistor is improved to over 90 dB. Finally, a 32 × 64 AMSPA (128 pixels per inch) is demonstrated with one-switch-transistor and one-synaptic phototransistor (1-T-1-PT) structure, achieving spatial chromatic enhancement and temporal trajectory imaging. These results reveal the feasibility of AMSPA for constructing artificial vision systems.

Optically enhanced organic phototransistors for adaptive image processing under complex light conditions

Effectively handling massive information in complex lighting conditions is crucial for security-focused machine vision, as it relies on precise image feature detection and encryption/decryption to ensure integrity and confidentiality. Traditional hardware, primarily based on complementary metal-oxide-semiconductor (CMOS) technology, struggles with the complexity of processing tasks around the clock. To address this challenge, a ternary organic heterostructure visuomorphic phototransistor was tailored for adaptive critical image processing. The light coupling induced by the porous heterostructural layer enhances the light absorption efficiency by 2.5-fold. Our phototransistor exhibits bidirectional photoresponse across the visible and near-infrared (NIR) spectral regions, enabling adaptive edge detection in varying lighting conditions with precision above 85 %. The phototransistor array facilitates image encryption/decryption with a superior accuracy of 12 %/90 % compared to existing counterparts. This ternary organic hetero-integration combines multiple response modes, enabling compact and efficient critical feature processing.

All-Optic Logical Operations Based on the Visible-Near Infrared Bipolar Optical Response.

The burgeoning need for extensive data processing has sparked enthusiasm for the development of a novel optical logic gate platform. In this study, junction field-effect phototransistors based on molybdenum disulfide/Germanium (MoS2/Ge) heterojunctions are constructed as optical logic units. This device demonstrates a positive photoresponse that is attributed to the photoconductivity effect occurring upon irradiation with visible (Vis) light. Under the illumination of near-infrared (NIR) optics with wavelengths within the communication band, the device shows a negative photoresponse, which is associated with the interlayer Coulomb interactions. The current state of the device can be effectively modulated as different logical states by precisely tuning the wavelength and power density of the optical. Within a 3×3 MoS2/Ge phototransistor array, five essentially all-optical logic gates ("AND," "OR," "NAND," "NOT," and "NOR") can be achieved in every signal unit. Furthermore, three complex all-optical logical operations are demonstrated by integrating two MoS2/Ge phototransistors in series. Compared to electronic designs, these all-optical logic devices offer a significant reduction in transistor number, with savings of 50-94% when implementing the above-mentioned functions. These results present opportunities for the development of photonic chips with low power consumption, high fidelity, and large volumes.

Highly Stretchable and Oriented Wafer-Scale Semiconductor Films for Organic Phototransistor Arrays.

Stretchable organic phototransistor arrays have potential applications in artificial visual systems due to their capacity to perceive ultraweak light across a broad spectrum. Ensuring uniform mechanical and electrical performance of individual devices within these arrays requires semiconductor films with large-area scale, well-defined orientation, and stretchability. However, the progress of stretchable phototransistors is primarily impeded by their limited electrical properties and photodetection capabilities. Herein, wafer-scale and well-oriented semiconductor films were successfully prepared using a solution shearing process. The electrical properties and photodetection capabilities were optimized by improving the polymer chain alignment. Furthermore, a stretchable 10 × 10 transistor array with high device uniformity was fabricated, demonstrating excellent mechanical robustness and photosensitive imaging ability. These arrays based on highly stretchable and well-oriented wafer-scale semiconductor films have great application potential in the field of electronic eye and artificial visual systems.

High-Detectivity and Broadband MoS2 Phototransistor Array by Coupling Negative Capacitance and Local Surface Plasmon Resonance Effects

High-Detectivity and Broadband MoS₂ Phototransistor Array by Coupling Negative Capacitance and Local Surface Plasmon Resonance Effects

Intrinsically stretchable phototransistors with polymer-QD-polymer multi-layered hybrid films for visible-NIR perspective electronic skin sensors

Stretchable phototransistors represent a crucial component in the development of skin-inspired optoelectronics. Although there have been significant advancements in the development of skin-like photosensitive semiconductors, technology for stretchable phototransistors that can detect a broad spectrum of wavelengths from near-infrared (NIR) to visible light is still in its early stages. This study introduces an intrinsically stretchable phototransistor employing hybrid semiconductor films consisting of polymer semiconductors (PSC) and quantum dots (QDs). The hybrid multi-layered semiconductor film (PSC/QDs/PSC) possesses wide-ranging color sensitivity from NIR to visible light, along with high photosensitivity and photoresponsivity. Furthermore, our phototransistor exhibits remarkable strain-insensitive, photo-response characteristics, maintaining performance even under 50% strain and enduring 10,000 strain cycles. Notably, the phototransistor array, featuring a distinctive dodecagon shape of source/drain electrodes, effectively responds to NIR and visible light stimuli, even when subjected to substantial areal strains of up to 38%.

Advanced IGZO Phototransistor Arrays: Enhancing Visible Light Detection Through Selectively Electrohydrodynamic Jet‐Printed Photocatalytic Layer Formation

AbstractExploring new horizons in phototransistors with an emphasis on mass customization is essential. Herein, a method for enhancing the performance of indium‐gallium‐zinc‐oxide (IGZO) phototransistors by incorporating a selectively formed tungsten trioxide (WO3) photocatalytic layer, utilizing electrohydrodynamic (EHD) jet‐printing is proposed. This approach aims to achieve significant manufacturing advantages and enhance functionality. An oxidizing solution of hydrogen peroxide (H2O2) doped with hydroxyethyl cellulose (HEC) is introduced to selectively oxidize tungsten (W) electrodes. In this mixture, H2O2 is responsible for the selective oxidation of W, whereas HEC contributes to the viscosity regulation and the formation of subgap states. The resulting selectively oxidized photocatalytic layer significantly expands its visible light absorption capacity to red light. Therefore, the optimized device, particularly under red light (635 nm) 5 mW mm−2, shows a remarkable enhancement in its optoelectronic characteristic: photoresponsivity increases from 29.71 to 124.54 A W−1, photosensitivity from 1.99 × 10‐1 to 1.79 × 104, and detectivity from 1.31 × 107 to 1.98 × 108 Jones compared to IGZO phototransistors without selectively oxidized photocatalytic layer. This advancement not only enhances the visible light detection capacity but also minimizes the persistent photoconductance issue inherent in IGZO devices. The demonstration of 6 × 6 phototransistor array illustrates the potential for image sensor applications, showcasing the practicality of mass customization.

Flexible retinomorphic vision sensors with scotopic and photopic adaptation for a fully flexible neuromorphic machine vision system

AbstractBioinspired neuromorphic machine vision system (NMVS) that integrates retinomorphic sensing and neuromorphic computing into one monolithic system is regarded as the most promising architecture for visual perception. However, the large intensity range of natural lights and complex illumination conditions in actual scenarios always require the NMVS to dynamically adjust its sensitivity according to the environmental conditions, just like the visual adaptation function of the human retina. Although some opto‐sensors with scotopic or photopic adaption have been developed, NMVSs, especially fully flexible NMVSs, with both scotopic and photopic adaptation functions are rarely reported. Here we propose an ion‐modulation strategy to dynamically adjust the photosensitivity and time‐varying activation/inhibition characteristics depending on the illumination conditions, and develop a flexible ion‐modulated phototransistor array based on MoS2/graphdiyne heterostructure, which can execute both retinomorphic sensing and neuromorphic computing. By controlling the intercalated Li+ ions in graphdiyne, both scotopic and photopic adaptation functions are demonstrated successfully. A fully flexible NMVS consisting of front‐end retinomorphic vision sensors and a back‐end convolutional neural network is constructed based on the as‐fabricated 28 × 28 device array, demonstrating quite high recognition accuracies for both dim and bright images and robust flexibility. This effort for fully flexible and monolithic NMVS paves the way for its applications in wearable scenarios.

High performance artificial visual perception and recognition with a plasmon-enhanced 2D material neural network

The development of neuromorphic visual systems has recently gained momentum due to their potential in areas such as autonomous vehicles and robotics. However, current machine visual systems based on silicon technology usually contain photosensor arrays, format conversion, memory and processing modules. As a result, the redundant data shuttling between each unit, resulting in large latency and high-power consumption, seriously limits the performance of neuromorphic vision chips. Here, we demonstrate an artificial neural network (ANN) architecture based on an integrated 2D MoS2/Ag nanograting phototransistor array, which can simultaneously sense, pre-process and recognize optical images without latency. The pre-processing function of the device under photoelectric synergy ensures considerable improvement of efficiency and accuracy of subsequent image recognition. The comprehensive performance of the proof-of-concept device demonstrates great potential for machine vision applications in terms of large dynamic range (180 dB), high speed (500 ns) and low energy consumption per spike (2.4 × 10−17 J).

Organic Heterojunction Phototransistors with Bi‐Directional Photoresponse for Vision Biomimetics

AbstractThe scientific community is very interested in artificial visual perception systems because of their neuromorphological capabilities, such as image recognition, learning, and memory. This study reports on an organic heterojunction ambipolar transistor with PTCDI‐C8/C8‐BTBT/PTCDI‐C8 sandwich structure. The proposed transistor efficiently transports both holes and electrons, with a current‐on‐switch ratio of ≈106. Furthermore, hole or electron carrier transmission mechanisms are constructed to achieve the controllable adjustment of bi‐directional photoresponse under identical light illumination conditions by adjusting the gate voltage (positive photoresponse for Vg = 30 V and negative photoresponse for Vg = −30 V). The basic synaptic behaviors are simulated under light illumination, and the power consumption of the device is 18.51 fJ per synaptic event, which is comparable to the energy required for biological synapses. Finally, the simulation of human visual adaptation is completed using the bi‐directional photoresponse effects of the organic heterojunction phototransistor array, which provides a novel idea for neuromorphic visual simulation.

Optical Microlithography of Perovskite Quantum Dots/Organic Semiconductor Heterojunctions for Neuromorphic Photosensors

AbstractHeterojunctions of perovskite quantum dots (QDs) and organic semiconductors (OSCs) can synergistically leverage the unique optoelectronic properties of different functional components to fabricate advanced optoelectronic devices, such as neuromorphic photosensors, by low‐cost solution processes. However, a long‐lasting challenge remains in micropatterning high‐density perovskite QDs/polymer OSCs heterojunction array with high yield and reliability due to the fragility of functional layers to organic solvents. High‐density and micro‐structure patterned organic neuromorphic photosensor arrays based on OSCs and QDs are thus rarely reported. Here, an effective cross‐linking microlithography strategy is reported to fabricate perovskite QDs/OSCs microstructure arrays. The fabricated CsPbBr3 QDs/(poly(2,5‐(2‐octyldodecyl)−3,6‐diketopyrrolopyrrole‐alt‐5,5‐(2,5‐di(thien‐2‐yl) thieno [3,2‐b] thiophene) (DPPDTT) planer heterojunctions phototransistor array presents minor device‐to‐device variation, high density (6500 devices cm−2), and high yield (almost 100%). The device array exhibits impressive merits as a neuromorphic photosensor, including a photosensitivity of 3.02 × 107, a responsivity up to 1.92 × 104 A W−1, a detectivity exceeding 1014 Jones, and a persistent photoconductivity. Moreover, an energy consumption as low as 27.9 aJ is achieved at an operating voltage of −0.0001 V. The potential application of the heterojunction neuromorphic photosensor array in motion perception is demonstrated in conjunction with a neural network.

A high-performance broadband phototransistor array of a PdSe2/SOI Schottky junction.

There is great interest in the incorporation of novel two-dimensional materials into Si-based technologies to realize multifunctional optoelectronic devices via heterogeneous integration. Here, we demonstrate a gate-tunable, self-driven, high-performance broadband phototransistor array based on a PdSe2/Si Schottky junction, which is fabricated by pre-depositing a semi-metallic PdSe2 film on a SOI substrate. In addition, thanks to the zero bandgap of the PdSe2 material and the PdSe2/Si vertical heterostructure, the prepared phototransistor exhibits pronounced photovoltaic properties in a wide spectral range from ultraviolet to near-infrared. The responsivity, specific detectivity and response time of the device at the incident light wavelength of 808 nm are 1.15 A W-1, 9.39 × 1010 Jones, and 27.1/40.3 μs, respectively, which are better than those of previously reported PdSe2-based photodetectors. The photoelectric performance can be further improved by applying an appropriate gate voltage to the phototransistor and the responsivity of the device increases to 1.61 A W-1 at VG = 5 V. We demonstrate the excellent imaging capabilities of a 4 × 4 array image sensor using PdSe2/SOI phototransistors under 375 nm, 532 nm, and 808 nm laser sources.

Retina-inspired sensor array for visual adaptation with wide dynamic range of 162 dB

The development of machine vision demands accurate image capture under different lighting conditions, which is crucial for perceiving the environment correctly. In this paper, we present a human-eye-inspired sensor based on quasi-two-dimensional perovskite and indium gallium zinc oxide phototransistor array. The sensor exhibits a light detection limit as low as 6.1 nW/cm2 with a responsivity of 5 × 105 A/W, capable of perceiving light in visible spectrum range. It demonstrates light adaptation under both dim and illuminated conditions, enhancing the contrast between images and ambient light, while achieving a dynamic range of 162 dB.

Silicon Nanowire Phototransistor Arrays for CMOS Image Sensor Applications.

This paper introduces a new design of silicon nanowire (Si NW) phototransistor (PT) arrays conceived explicitly for improved CMOS image sensor performance, and comprehensive numerical investigations clarify the characteristics of the proposed devices. Each unit within this array architecture features a top-layer vertical Si NW optimized for the maximal absorption of incoming light across the visible spectrum. This absorbed light generates carriers, efficiently injected into the emitter-base junction of an underlying npn bipolar junction transistor (BJT). This process induces proficient amplification of the output collector current. By meticulously adjusting the diameters of the NWs, the PTs are tailored to exhibit distinct absorption characteristics, thus delineating the visible spectrum's blue, green, and red regions. This specialization ensures enriched color fidelity, a sought-after trait in imaging devices. Notably, the synergetic combination of the Si NW and the BJT augments the electrical response under illumination, boasting a quantum efficiency exceeding 10. In addition, by refining parameters like the height of the NW and gradient doping depth, the proposed PTs deliver enhanced color purity and amplified output currents.

InP Quantum Dots Tailored Oxide Thin Film Phototransistor for Bioinspired Visual Adaptation

AbstractThe exploration of bionic neuromorphic chips, capable of processing sensory data in a human‐like manner, is both a trend and a challenge. There is a strong demand for phototransistors that offer broadband in‐sensor adaptability. This study introduces a bioinspired vision sensor based on InP quantum dots (QDs)/InSnZnO hybrid phototransistors. This novel design combines the excellent electrical transportation features of oxide semiconductors with the superior optoelectronic response of InP QDs. The resulting hybrid devices exhibit exceptional gate controllability and a robust visible‐light response. These characteristics enable the emulation of multiple functions of the human visual system and the accommodation of varying light intensity environments. Furthermore, the phototransistor array successfully replicates the scotopic and photopic adaptation recognition behaviors of the human retina. Notably, the device demonstrates faultless competency in image processing, achieving an impressive 93% accuracy for digit recognition. These findings contribute to the advancement of bionic neuromorphic chips and offer promising opportunities for future developments in the bioinspired visual system.

Colorimetric Multigas Sensor Arrays and an Artificial Olfactory Platform for Volatile Organic Compounds.

Herein, we develop colorimetric multigas sensor arrays assembling chemo-reactive fluorescent patch arrays and 10 × 10 indium gallium zinc oxide phototransistor arrays and apply them to an artificial olfactory platform to recognize five different volatile organic compounds (VOCs). Porous nanofibers, coupled with two organic emitters and emitting fluorescence, rapidly respond to gas-phased VOCs and offer unique fluorescent patterns associated with particular gas conditions, including gas kinds, concentrations, and exposure times by forming patch arrays with different fluorophore component ratios. These VOC-induced fluorescent patterns could be quantified and amplified by indium gallium zinc oxide (IGZO) phototransistor arrays functioning as a signal-generating component, resulting in gas-fingerprint patterns regarding electrical signals. Thus, the pattern library associated with VOCs and their concentration enables us to determine each airborne analyte as the artificial olfactory platform. Therefore, this system could achieve rapid, early quantitative recognition of hazardous gases and be applied as a preventative, portable, and wearable multigas identifier in various fields.