High voltage metal oxide thin film transistors to drive arrays of dielectric elastomer actuators

This thesis advances the field of high-voltage thin film transistors (HVTFTs) and dielectric elastomer actuators (DEAs) by demonstrating a strategy for low-voltage addressing of an array of high voltage soft actuators suspended on a flexible substrate. First, I present the first HVTFTs operating at 1 kV drain-source voltage, switching with an on-off ratio of 20 at 80 V gate-source voltage. The HVTFTs can operate at high voltage thanks to geometrical features increasing the breakdown voltage: a thick gate dielectric composed of a bilayer of alumina (100 nm) and Parylene-C (1 um), a long semiconducting channel (500 um), and a 150 &mlong non-gated region between the drain and the gate electrode called the offset gate. The use of an amorphous oxide semiconductor (AOS), zinc tin oxide (ZTO), enables a high on-currents of 0.1 mA. The ZTO was synthesized by a sol-gel process after spin-coating on a flexible polyimide substrate, previously passivated with alumina. I optimized the HVTFT switching properties by doping the ZTO layer with yttrium (5%). It improved the on-off ratio up to 1000 at 500 V operation voltage by decreasing the leakage current down to 100 nA. Then, I show the first integration of HVTFTs with DEAs. My ZTO HVTFTs switch DEAs on and off with only 30 V gate voltage under a bias voltage of 1.4 kV. The system time response in 50 ms. The demonstrator is a 4x4 array of diaphragm DEAs. A layer of 4x4 DEAs is suspended over a layer of 4x4 HVTFTs built on flexible polyimide. The DEAs and the HVTFTs were interconnected thanks to a flexible PCB in a resistive load inverter circuit architecture. A flexible 3D printed chamber was constantly biasing the DEA diaphragms with a back-pressure. The DEAs were made of PDMS and the active region is defined by overlapping carbon-PDMS electrodes. The device operates down to a 5mm radius of curvature. Finally, I demonstrate latching of the HVTFT and the DEA by using triboelectric sensors. Under a constant 500 V circuit bias, the control of the HVTFT gate with triboelectric generators enabled 4s latching of the inverter output voltage at 470 V for the off-state and at 120 V for the on-state. The latching of the DEAs with the HVTFT circuit finally proves that this approach can lead to a bistable control of DEAs. This PhD thesis results show that my HVTFTs are versatile components usable not only to address DEAs but also to interface low voltage sensors with high voltage actuators

Flexible 1kV thin-film transistor driving out-of-plane dielectric elastomer actuator

This work demonstrates dielectric elastomer actuators controlled by the world's first thin-film transistors on flexible substrate operating at 1kV, thereby enabling locally switching high-voltages on DEAs using a low control voltage. The high voltages required to drive DEAs limit their integration in complex systems, such as high resolution haptic displays and multiple-degree-of-freedom robotics. We report here a top-gate, thin-film transistor (TFT) with coplanar electrodes specifically designed to drive DEAs. The TFTs are fabricated on flexible polyimide, using solution-processed zinc-tin oxide, offset gate and thick dielectric bilayer of Alumina and Parylene. The TFT switches reliably at up to 1kV, outperforming on this metric all published high-voltage TFTs. The on-off current ratio ranges from 20 to 200, the saturation mobility is 0.1cm2/Vs, and the threshold voltage is 10V. Our DEAs are designed for maximal actuation strain at 1kV, to match the maximal voltage of the TFTs. The DEA is a diaphragm actuator: a suspended non-prestretched membrane with electrodes on both sides. The circular electrode has a 5 mm diameter and the silicone membrane is 17um thick. A backpressure of 50mbar is applied to the membrane. The TFT is wired in parallel with the DEA. A change of out-of-plane displacement of 350um is achieved with 30V applied to the gate, for a circuit bias voltage of 1.4kV. The TFT + DEA operate reliably for several weeks

Flexible Zinc-Tin Oxide Thin Film Transistors Operating at 1 kV for Integrated Switching of Dielectric Elastomer Actuators Arrays

Flexible high-voltage thin- lm transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a exible array of 16 independent actuators. To allow for high-voltage operation, the HVTFT implements a zinc–tin oxide channel, a thick dielectric stack, and an offset gate. At a source–drain bias of 1 kV, the HVTFT has a 20 μA on-current at a gate voltage bias of 30 V. Their electrical characteris- tics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high-voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA de ection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal-oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics

Multi-dimensional imaging and phenotyping of C. elegans embryos via an automated microfluidic device

We introduce a microfluidic platform for automated on-chip worm culture, creation of synchronized embryo microarrays, and long-term parallel live imaging of Caenorhabditis elegans embryos. Our device allows studying well-defined embryo populations at unprecedented spatio-temporal resolution, via fully automated multi-dimensional imaging, covering six independent dimensions: the 3 spatial coordinates, development time, exposure duration/type (brightfield, fluorescent), and embryo number in the microarray. We successfully employed our platform to investigate the impact of perturbations of the mitochondrial functions on C.elegans embryogenesis. Our analyses revealed that specific mitochondrial stresses trigger a mitochondrial unfolded protein response (UPRmt) in the embryos. These observations are the first proof that the UPRmt molecular pathway is functional during C.elegans embryogenesis