Advanced Sensing Systems Exploiting the Integration of Flexible and Large-Area TFTs with Si-CMOS Technology

This manuscript provides an overview of recent advances in sensing systems built by heterogeneous integration of Flexible and Large-Area electronics with Si-CMOS ICs. This approach enables unprecedented form factors required in e.g., wearable and biomedical applications. However, the integration of different technologies poses important challenges from both the electrical and the manufacturing perspective. Architectural and circuit solutions to overcome some of the main integration hurdles are discussed. Furthermore, three relevant emerging applications are presented.</p

Indoor fall detector based on Doppler radar

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Embedded DSP-based Telehealth Radar System for Remote In-door Fall Detection

Telehealth systems and applications are extensively investigated nowadays to enhance the quality-of-care and, in particular, to detect emergency situations and to monitor the well-being of elderly people, allowing them to stay at home independently as long as possible. In this paper, an embedded telehealth system for continuous, automatic, and remote monitoring of real-time fall emergencies is presented and discussed. The system, consisting of a radar sensor and base station, represents a cost-effective and efficient healthcare solution. The implementation of the fall detection data processing technique, based on the least-square support vector machines, through a digital signal processor and the management of the communication between radar sensor and base station are detailed. Experimental tests, for a total of 65 mimicked fall incidents, recorded with 16 human subjects (14 men and two women) that have been monitored for 320 min, have been used to validate the proposed system under real circumstances. The subjects' weight is between 55 and 90 kg with heights between 1.65 and 1.82 m, while their age is between 25 and 39 years. The experimental results have shown a sensitivity to detect the fall events in real time of 100% without reporting false positives. The tests have been performed in an area where the radar's operation was not limited by practical situations, namely, signal power, coverage of the antennas, and presence of obstacles between the subject and the antennas.status: publishe

An EMG Interface Comprising a Flexible a-IGZO Active Electrode Matrix and a 65-nm CMOS IC

n this work, a 4× 4 active electrode (AE) matrix integrated on a flexible foil substrate to monitor muscular contraction is presented. The electrodes and their front ends (FEs) (i.e., AEs) are implemented on foil in amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) technology and interfaced with a custom 65-nm CMOS chip where analog-to-digital conversion and serial transmission of data from multiple channels are performed. On-foil frequency multiplexing and conversion to current domain are used to transmit to the silicon (Si)-IC, all the signals coming from a column of electrodes via a single output. This strategy enables interfacing the 26-V-supply flexible electronics with the 1.2-V-supply CMOS IC, while reducing the number of interconnects and Si area devoted to pads. The a-IGZO FE includes an integrated switched-capacitor high-pass input filter offering a 25–40- MΩ impedance in the band of interest. Each AE on foil occupies 4× 4 mm, enabling electromyography (EMG) measurements with millimeter (mm)-range resolution. The a-IGZO amplifier in the AE, with its intrinsic bandpass response, achieves a process and temperature-insensitive 20-dB in-band gain and a 23-dB dc rejection. The back-end Si-IC can compensate variable bias currents and offsets from the flexible FE exploiting an offset-compensated trans-impedance amplifier (TIA) with 50-dB-dc rejection and negligible noise contribution. The a-IGZO FE alone achieves 20- μA /V gain, 30-kHz bandwidth (BW), 55- μVrms input-referred noise, consuming 5 mW. The system has been validated in vivo extracting the muscle fiber conduction velocity from the tibialis anterior of a volunteer

Analogue Frontend Amplifiers for Bio-Potential Measurements Manufactured With a-IGZO TFTs on Flexible Substrate

Three novel differential amplifier topologies using double gate a-IGZO TFTs on flexible substrate are presented in this paper. The designs exploit positive feedback and a load with self-biased top gate to achieve the highest static gain in single stage a-IGZO amplifiers reported to date. After fabrication, the three amplifiers exhibit respectively a static gain of 14 dB, 21.5 dB and 30 dB, with a bandwidth of 2 kHz, 400 Hz, and 150 Hz. Also, for each circuit the input referred noise has been measured to be 420 μVrms, 195 μVrms and 146 μVrms, respectively. Based on these results, the a-IGZO amplifier providing the highest gain is suitable as front-end for heart rate measurements and, with some further optimization verified in simulation, can also be used for other bio-potential applications, like electro hysterogram and electro cardiogram

Unified physical DC model of staggered amorphous InGaZnO transistors

In this paper, we propose a unified physical model of InGaZnO [amorphous indium-gallium-zinc-oxide (a-IGZO)] thin-film transistors (TFTs) accounting for both charge injection at the contact and charge transport within the channel. We extract the current-voltage characteristics of the injecting contact from the measurements of a-IGZO TFTs fabricated on plastic foil. We show that the charge injection depends on both the drain and the gate voltages. We model the charge injection in staggered a-IGZO TFTs basing on the thermionic emission-diffusion theory including the charge carrier-dependent electron velocity due to the trap states in the subgap of the a-IGZO semiconductor. Combining the charge injection model with a charge transport model, we accurately and consistently describe the measurements of staggered a-IGZO TFTs with channel-length scaling from 200 μm to 15 μm. The proposed unified model is implemented in a circuit simulator and used to design unipolar inverters. The good agreement between simulations and measurements of the inverters further confirms the effectiveness of the proposed approach

Compact physical model of a-IGZO TFTs for circuit simulation

Amorphous InGaZnO (a-IGZO) is a candidate material for thin-film transistors (TFTs) owing to its large electron mobility. The development of high functionality circuits requires accurate and efficient circuit simulation that, in turn, is based on compact physical a-IGZO TFTs models. Here we propose a compact physical-based and analytical model of the drain current of a-IGZO TFTs. The model accounts for both trapped and free charges by means of an effective density of states that accurately approximate the actual a-IGZO density of states in the energy range relevant for the TFT operation. The model is implemented in a circuit simulator and it is validated with the measurements of both coplanar and staggered a-IGZO TFTs fabricated on flexible substrates

Physical-based analytical model of flexible a-IGZO TFTs accounting for both charge injection and transport

Here we show a new physical-based analytical model of a-IGZO TFTs. TFTs scaling from L=200 μm to L=15 μm and fabricated on plastic foil are accurately reproduced with a unique set of parameters. The model is used to design a zero-\u3cbr/\u3eVGS inverter. It is a valuable tool for circuit design and technology characterization