Yingzhe Hu

Large-Scale Sensing System Combining Large-Area Electronics and CMOS ICs for Structural-Health Monitoring

Early-stage damage detection for bridges requires continuously sensing strain over large portions of the structure, yet with centimeter-scale resolution. To achieve sensing on such a scale, this work presents a sensing sheet that combines CMOS ICs, for sensor control and readout, with large-area electronics (LAE), for many-channel distributed sensing and data aggregation. Bonded to a structure, the sheet thus enables strain sensing scalable to high spatial resolutions. In order to combine the two technologies in a correspondingly scalable manner, non-contact interfaces are used. Inductive and capacitive antennas are patterned on the LAE sheet and on the IC packages, so that system assembly is achieved via low-cost sheet lamination without metallurgical bonds. The LAE sheet integrates thin-film strain gauges, thin-film transistors, and long interconnects on a 50-μm-thick polyimide sheet, and the CMOS ICs integrate subsystems for sensor readout, control, and communication over the distributed sheet in a 130 nm process. Multi-channel strain readout is achieved with sensitivity of 18 μStrain RMS at a readout energy of 270 nJ/measurement, while the communication energy is 12.8 pJ/3.3 pJ per bit (Tx/Rx) over a distance of 7.5 m.

A Self-Powered System for Large-Scale Strain Sensing by Combining CMOS ICs With Large-Area Electronics

We present a 2nd-generation system for high-resolution structural-health monitoring of bridges and buildings. The system combines large-area electronics (LAE) and CMOS ICs via scalable interfaces based on inductive and capacitive coupling. This enables architectures where the functional strengths of both technologies can be leveraged to enable large-scale strain sensing scalable to cm resolution yet over large-area sheets. The system consists of three subsystems: (1) a power-management subsystem, where LAE is leveraged for solar-power harvesting, and CMOS is leveraged for power conversion and regulation; (2) a sensing subsystem, where LAE is leveraged for dense strain sensing, and CMOS is leveraged for multi-sensor acquisition; and (3) a communication subsystem, where LAE is leveraged for long-range interconnects, and CMOS is leveraged for low-power transceivers. The power-management subsystem achieves 30% efficiency for DC-AC power inversion and inductive power delivery to the CMOS IC and 80.5% overall efficiency for generating three voltages via DC-DC converters. The sensing subsystem has a readout noise level of 23 μStrainRMS (141 μStrainRMS including sensor noise), at an energy/meas. of 148 nJ and 286 nJ for readout and sensor-accessing control, respectively. The communication subsystem achieves an energy/bit of 14.6 pJ/4.3 pJ (Tx/Rx) at a distance of 7.5 m and a data rate of 2 Mb/s.

Enabling Scalable Hybrid Systems: Architectures for Exploiting Large-Area Electronics in Applications

By enabling diverse and large-scale transducers, large-area electronics raises the potential for electronic systems to interact much more extensively with the physical world than is possible today. This can substantially expand the scope of applications, both in number and in value. But first, translation into applications requires a base of system functions (instrumentation, computation, power management, communication). These cannot be realized on the desired scale by large-area electronics alone. It is necessary to combine large-area electronics with high-performance, high-efficiency technologies, such as crystalline silicon CMOS, within hybrid systems. Scalable hybrid systems require rethinking the subsystem architectures from the start by considering how the technologies should be interfaced, on both a functional and physical level. To explore platform architectures along with the supporting circuits and devices, we consider as an application driver, a self-powered sheet for high-resolution structural health monitoring (of bridges and buildings). Top-down evaluation of design alternatives within the hybrid design space and pursuit of template architectures exposes circuit functions and device optimizations traditionally overlooked by bottom-up approaches alone.

Thin-film circuits for scalable interfacing between large-area electronics and CMOS ICs

Hybrid systems based on large-area electronics (LAE) and CMOS ICs aim to exploit the complementary strengths of the two technologies: the scalability of LAE for forming interconnects and transducers (for sensing and energy harvesting), and the energy efficiency of CMOS for instrumentation and computation. The viability of large-scale systems depends on maximizing the robustness and minimizing the number of interfaces between the LAE and CMOS domains. To maximize robustness, inductive and capacitive coupling has been explored, avoiding the need for metallurgical bonding [1]. To minimize the number of interfaces, a method to access and readout individual sensors via minimal coupling channels, is crucial. In this abstract, we present a thin-film transistor (TFT) based scanning circuit that requires only three capacitively-coupled control signals from the IC to sequentially access an arbitrarily large number of LAE sensors, enabling a single readout interface (Fig. 1). A key attribute of the presented circuit is the low power consumption, which remains nearly constant even as the number of sensors scales.

Flexible solar-energy harvesting system on plastic with thin-film LC oscillators operating above f t for inductively-coupled power delivery

This paper presents an energy-harvesting system consisting of amorphous-silicon (a-Si) solar cells and thin-film-transistor (TFT) power circuits on plastic. Along with patterned planar inductors, the TFTs realize an LC-oscillator that provides power inversion of the DC solar-module output, enabling a low-cost sheet for inductively-coupled wireless charging of devices. Despite the low performance of the TFTs (ft=1.3MHz at a voltage of 15V), the oscillator can operate above 2MHz by incorporating the device parasitics into the resonant tank. This enables increased quality factor for the planar inductors, improving the power-transfer efficiency and the power delivered. With 3cm-radius single- and double-layer inductors, the system achieves 22.6% and 31% power-transfer efficiency (approaching the analytically-predicted bound), while the power delivered is 20mW and 22mW.

12.2 3D gesture-sensing system for interactive displays based on extended-range capacitive sensing

Capacitive touch screens have enabled compelling interfaces for displays. Three-dimensional (3D) sensing, where user gestures can also be sensed in the out-of-plane dimension to distances of 20 to 30cm, represents new interfacing possibilities that could substantially enrich user experience. The challenge is achieving sensitivity at these distances when sensing the small capacitive perturbations caused by user interaction with sensing electrodes. Among capacitive-sensing approaches, self capacitance enables substantially greater distance than mutual capacitance (i.e., between electrodes), but can suffer from ghost effects during multi-touch. For gesture recognition, however, processing via classifiers can overcome such effects, enabling a rich dictionary of gestures. Nonetheless, the sensing distance of such systems has been too limited for 3D sensing.

A super-regenerative radio on plastic based on thin-film transistors and antennas on large flexible sheets for distributed communication links

Large-area electronics presents new form factors, enabling ubiquitous systems that are flexible and capable of scaling to very large areas. By processing thin-film transistors (TFTs) at low temperatures on plastic (using organics, amorphous silicon, metal oxides, etc.), blocks such as ADCs, amplifiers, and processors can be realized [1,2]; however, aside from short-range RFID tags [3], wireless links for long-range communication have not been achieved. A key challenge is that wireless systems typically depend on the ability to generate and operate at high frequencies, yet TFTs are limited to very low performance (ft ~1MHz). Specifically, the challenge is low device gm, due to low mobility and limited gate-dielectric scalability, as well as high device capacitance, due to limited feature scalability and large overlaps for alignment margining on flexible substrates. This work presents a super-regenerative (SR) transceiver with integrated antenna on plastic that leverages the attribute of large area to create highquality passives; this enables resonant TFT circuits at high frequencies (near ft) and allows for large antennas, maximizing the communication distance. The resulting carrier frequency is 900kHz, and the range is over 12m (at 2kb/s). As shown in Fig. 25.10.1, this will enable sheets with integrated arrays of radio frontends for distributing a large number of communication links over large areas.

Integrated all-silicon thin-film power electronics on flexible sheets for ubiquitous wireless charging stations based on solar-energy harvesting

With the explosion in the number of battery-powered portable devices, ubiquitous powering stations that exploit energy harvesting can provide an extremely compelling means of charging. We present a system on a flexible sheet that, for the first time, integrates the power electronics using the same thin-film amorphous-silicon (a-Si) technology as that used for established flexible photovoltaics. This demonstrates a key step towards future large-area flexible sheets which could cover everyday objects, to convert them into wireless charging stations. In this work, we combine the thin-film circuits with flexible solar cells to provide embedded power inversion, harvester control, and power amplification. This converts DC outputs from the solar modules to AC power for wireless device charging through patterned capacitive antennas. With 0.5-2nF transfer antennas and solar modules of 100cm2, the system provides 47-120μW of power at 11-22% overall power-transfer efficiency under indoor lighting.

A Complete Fully Thin-Film PV Harvesting and Power-Management System on Plastic With On-Sheet Battery Management and Wireless Power Delivery to Off-sheet Loads

Large-area electronics enables the creation of systems with transformational capabilities and form factors. Through the ability to integrate thin-film photovoltaics, batteries, and active transistors, complete power-management subsystems addressing a wide range of applications can also be created. We present, for the first time, a fully flexible system integrating amorphous silicon (a-Si) solar modules with Li-ion thin-film batteries and circuits that are based on a-Si thin-film transistors for battery management and wireless power delivery. A fabricated prototype of the entire system on a plastic sheet is demonstrated. Using a 240 cm2 solar module under indoor lighting conditions (~400 μW/cm2), the system is measured to provide 1) dc power (~1 mW) to on-sheet loads and 2) ac power (~10 mW) to off-sheet loads through wireless transmission. Four Li-ion batteries are used for on-sheet energy storage with a battery-management system ensuring discharging at permissible levels, while imposing minimal off-state current (<;360 nA).

Hybrid Amorphous/Nanocrystalline Silicon Schottky Diodes for High Frequency Rectification

We report hybrid amorphous (a-Si)/nanocrystalline (nc-Si) Schottky diodes for rectification at high frequencies. All fabrication steps are done at , making them compatible with processing on plastic. The diodes have a high current density (5 A/cm2 at 1 V and 100 A/cm2 at 2 V) and on-to-off current ratio (over 1000 for bias voltages of 1/-8 V). A 0.01- mm2 hybrid diode has a series resistance of 200 Ω and a capacitance of 7 pF, leading to a cutoff frequency of 110 MHz. As a half-wave rectifier driving a parallel 1- MΩ resistive and 100-nF capacitive load, the dc rectified voltage drops at frequencies , with a -3 dB point at 70 MHz.