Multimodal transistors as ReLU activation functions in physical neural network classifiers

Artificial neural networks (ANNs) providing sophisticated, power-efficient classification are finding their way into thin-film electronics. Thin-film technologies require robust, layout-efficient devices with facile manufacturability. Here, we show how the multimodal transistor’s (MMT’s) transfer characteristic, with linear dependence in saturation, replicates the rectified linear unit (ReLU) activation function of convolutional ANNs (CNNs). Using MATLAB, we evaluate CNN performance using systematically distorted ReLU functions, then substitute measured and simulated MMT transfer characteristics as proxies for ReLU. High classification accuracy is maintained, despite large variations in geometrical and electrical parameters, as CNNs use the same activation functions for training and classification

Ultra-compact multi-level digital-to-analog converter based on linear multimodal thin-film transistors

International audienceA new device, the Multimodal Transistor (MMT), separates charge injection from conduction and achieves a linear dependence of drain current on its control gate voltage. This functionality is used to implement a highly compact digital-to-analog-converter, capable of performing 3-level, 3-bit conversion with minimal error (1.2% of LSB). © 2020 SID

Engineering current-voltage linearity in TFTs for analog and neuromorphic computing

International audienceMany emerging analog and neuromorphic applications would benefit from a fully linear dependence of a transistor's output on its input for reduced distortion and facile design of linear functions. We show how a new TFT structure, the multimodal transistor, can achieve a linearly dependent drain current in saturation (constant transconductance) with direct proportionality over a large range of input voltages

Turn-off mechanisms in thin-film source-gated transistors with applications to power devices and rectification

We describe the physics of the turn-off mechanism in source-gated transistors (SGTs), which is distinct from that of conventional thin-film field-effect transistors and allows significantly lower off currents, particularly in depletion-mode devices. The “n-type” SGT enters its off state when the potential applied across the semiconductor layer is decreased to low positive values or made negative through the applied gate bias, thus impeding charge injection from the source contact. Measurements on polysilicon devices were supported with TCAD simulations using Silvaco Atlas. Alongside the other known benefits of SGTs, including low saturation voltage, tolerance to process variations, and high intrinsic gain, the ability to efficiently block current at high negative gate voltages suggests that these devices would be ideal elements in emerging thin-film power management and rectification circuits

The multimodal thin-film transistor (Mmt): A versatile low-power and high-gain device with inherent linear response

International audienceA new device, the Multimodal Transistor (MMT), separates charge injection from conduction. With design optimization, it can achieve a constant transconductance with independent on/off switching of output current. This functionality has ample applications in energy efficient analog computation and hardware learning. © 2020 SID

Investigation on icp-cvd as a polyvalent low cost technology dedicated to low temperature μ-si tft prototyping.

International audienceA Corial Inductively Coupled Plasma Chemical Vapor Deposition (ICP-CVD) system has been investigated to produce un-doped and doped μ-Si layers, as well as insulators, leading to a general capability of performing N and P type TFTs. This enables to develop rapid prototyping of TFTs. Resistivity of layers and TFT issues from ICP-CVD have been electrically characterized. © 2020 SID

Evidence of Improved Thermal Stability via Nanoscale Contact Engineering in IGZO Source-Gated Thin-Film Transistors

Despite rapidly expanding interest in thin-film source-gated transistors (SGTs), the high temperature dependence of drain current (TDDC) in devices comprising Schottky source barriers is delaying wide adoption. To reduce this effect, alternative source designs have been theorized. Specifically, introducing additional nanoscale layers at the source contact should facilitate tunneling of charge carriers at the Fermi energy level with negligible TDDC. Here, we fabricate amorphous In₂Ga₂ZnO₇ tunnel-contact SGTs (TCSGTs) with three times lower TDDC than polysilicon transistors with Schottky contacts. Numerical simulations help elucidate the control mechanisms. We show that the potential profile across the semiconductor in the bulk of the source-gate overlap region determines injection current, and the introduction of a thin interfacial layer at the contact reduces the role of the contact metal work function in current control and associated temperature effects. This device architecture adds improved thermal stability to the long list of SGT benefits, including low voltage saturation, power-efficient operation, high intrinsic gain, device-to-device uniformity, and robustness to mechanical and electrical stress

In-Ga-Zn-O Source-Gated Transistors with 3nm SiO2Tunnel Layer on a Flexible Polyimide Substrate

We report the first In-Ga-Zn-O source-gated transistors on a flexible polyimide film. Our findings show that using Au contacts and the incorporation of an ultrathin SiO2 tunnel layer facilitate contact-controlled operation, distinct from conventional thin-film transistors with Ti contacts. This was confirmed by early saturation in the output characteristics and the very low saturation voltage change over a gate voltage change of < 0.1 V/V which agrees well with the theoretical saturation coefficient of ≈ 0.1

Compact Source-Gated Transistor Analog Circuits for Ubiquitous Sensors

Silicon-based digital electronics have evolved over decades through an aggressive scaling process following Moore's law with increasingly complex device structures. Simultaneously, large-area electronics have continued to rely on the same field-effect transistor structure with minimal evolution. This limitation has resulted in less than ideal circuit designs, with increased complexity to account for shortcomings in material properties and process control. At present, this situation is holding back the development of novel systems required for printed and flexible electronic applications beyond the Internet of Things. In this work we demonstrate the opportunity offered by the source-gated transistor's unique properties for low-cost, highly functional large-area applications in two extremely compact circuit blocks. Polysilicon common-source amplifiers show 49 dB gain, the highest reported for a two-transistor unipolar circuit. Current mirrors fabricated in polysilicon and InGaZnO have, in addition to excellent current copying performance, the ability to control the temperature dependence (degrees of positive, neutral or negative) of output current solely by choice of relative transistor geometry, giving further flexibility to the design engineer. Application examples are proposed, including local amplification of sensor output for improved signal integrity, as well as temperature-regulated delay stages and timing circuits for homeostatic operation in future wearables. Numerous applications will benefit from these highly competitive compact circuit designs with robust performance, improved energy efficiency and tolerance to geometrical variations: sensor front-ends, temperature sensors, pixel drivers, bias analog blocks and high-gain amplifiers