H.S.Philip Wong, Postdoctoral Faculty Sponsor
- Programmable a-InGaZnO gate array with laser-induced forward transfer FLEXIBLE AND PRINTED ELECTRONICS 2021; 6 (1)
- Stand-Alone Intrinsically Stretchable Electronic Device Platform Powered by Stretchable Rechargeable Battery ADVANCED FUNCTIONAL MATERIALS 2020
A Flexible 3D Organic Preamplifier for a Lactate Sensor
Organic transistors are promising platforms for wearable biosensors. However, the strategies to improve signal amplification have yet to be determined, particularly regarding biosensors that generate very weak signals. In this study, an organic voltage amplifier is presented for a lactate sensor on flexible plastic foil. The preamplifier is based on a 3D complementary inverter, which is achieved by vertically stacking complementary transistors with a shared gate between them. The shared gate is extended and functionalized with a lactate oxidase enzyme to detect lactate. The sensing device successfully detects the lactate concentration in the human sweat range (20-60 mm) with high sensitivity (6.82 mV mm-1 ) due to high gain of its amplification. The 3D integration process is cost-effective as it is solution-processable and doubles the number of transistors per unit area. The device presented in this study would pave the way for the development of high-gain noninvasive sweat lactate sensors that can be wearable.
View details for DOI 10.1002/mabi.202000144
View details for Web of Science ID 000544611800001
View details for PubMedID 32613734
- Phase-Separated, Printed Organic Thin-Film Transistor-Based Nonvolatile Memory with Enhanced Data Retention ADVANCED MATERIALS TECHNOLOGIES 2020; 5 (7)
- Reliable inkjet contact metallization on printed polymer semiconductors for fabricating staggered TFTs APPLIED PHYSICS LETTERS 2020; 116 (15)
Artificial multimodal receptors based on ion relaxation dynamics.
Science (New York, N.Y.)
2020; 370 (6519): 961–65
Human skin has different types of tactile receptors that can distinguish various mechanical stimuli from temperature. We present a deformable artificial multimodal ionic receptor that can differentiate thermal and mechanical information without signal interference. Two variables are derived from the analysis of the ion relaxation dynamics: the charge relaxation time as a strain-insensitive intrinsic variable to measure absolute temperature and the normalized capacitance as a temperature-insensitive extrinsic variable to measure strain. The artificial receptor with a simple electrode-electrolyte-electrode structure simultaneously detects temperature and strain by measuring the variables at only two measurement frequencies. The human skin-like multimodal receptor array, called multimodal ion-electronic skin (IEM-skin), provides real-time force directions and strain profiles in various tactile motions (shear, pinch, spread, torsion, and so on).
View details for DOI 10.1126/science.aba5132
View details for PubMedID 33214277
- Compact modelling and SPICE simulation for three-dimensional, inkjet-printed organic transistors, inverters and ring oscillators JOURNAL OF PHYSICS D-APPLIED PHYSICS 2019; 52 (44)
Flexible Pressure-Sensitive Contact Transistors Operating in the Subthreshold Regime
ACS APPLIED MATERIALS & INTERFACES
2019; 11 (34): 31111–18
Organic thin-film transistor (TFT)-based pressure sensors have received huge attention for wearable electronic applications such as health monitoring and smart robotics. However, there still remains a challenge to achieve low power consumption and high sensitivity at the same time for the realization of truly wearable sensor systems where minimizing power consumption is significant because of limited battery run time. Here, we introduce a flexible pressure-sensitive contact transistor (PCT), a new type of pressure-sensing device based on organic TFTs for next-generation wearable electronic skin devices. The PCT consists of deformable S/D electrodes integrated on a staggered TFT. The deformable S/D electrodes were fabricated by embedding conducting single-walled carbon nanotubes on the surface of microstructured polydimethylsiloxane. Under pressure loads, the deformation of the electrodes on an organic semiconductor layer leads modulation of drain current from variation in both the channel geometry and contact resistance. By strategic subthreshold operation to minimize power consumption and increase the dominance of contact resistance because of gated Schottky contact, the PCT achieves both ultralow power consumption (order of 101 nW) and high sensitivity (18.96 kPa-1). Finally, we demonstrate a 5 × 5 active matrix PCT array on a 3 μm-thick parylene substrate. The device with ultralow power consumption and high sensitivity on a biocompatible flexible substrate makes the PCT promising candidate for next-generation wearable electronic skin devices.
View details for DOI 10.1021/acsami.9b09636
View details for Web of Science ID 000484073400066
View details for PubMedID 31373197
- Static and Dynamic Response Comparison of Printed, Single- and Dual-Gate 3-D Complementary Organic TFT Inverters IEEE ELECTRON DEVICE LETTERS 2019; 40 (8): 1277–80
- Bistaggered Contact Geometry for Symmetric Dual-Gate Organic TFTs IEEE TRANSACTIONS ON ELECTRON DEVICES 2019; 66 (7): 3118–23
- Parylene copolymer gate dielectrics for organic field- effect transistors JOURNAL OF MATERIALS CHEMISTRY C 2019; 7 (21): 6251–56
Three-dimensional monolithic integration in flexible printed organic transistors
2019; 10: 54
Direct printing of thin-film transistors has enormous potential for ubiquitous and lightweight wearable electronic applications. However, advances in printed integrated circuits remain very rare. Here we present a three-dimensional (3D) integration approach to achieve technology scaling in printed transistor density, analogous to Moore's law driven by lithography, as well as enhancing device performance. To provide a proof of principle for the approach, we demonstrate the scalable 3D integration of dual-gate organic transistors on plastic foil by printing with high yield, uniformity, and year-long stability. In addition, the 3D stacking of three complementary transistors enables us to propose a programmable 3D logic array as a new route to design printed flexible digital circuitry essential for the emerging applications. The 3D monolithic integration strategy demonstrated here is applicable to other emerging printable materials, such as carbon nanotubes, oxide semiconductors and 2D semiconducting materials.
View details for DOI 10.1038/s41467-018-07904-5
View details for Web of Science ID 000454757900005
View details for PubMedID 30604747
View details for PubMedCentralID PMC6318314
Parylene-Based Double-Layer Gate Dielectrics for Organic Field-Effect Transistors
ACS APPLIED MATERIALS & INTERFACES
2018; 10 (44): 37767–72
We demonstrate high-performance and stable organic field-effect transistors (OFETs) using parylene-based double-layer gate dielectrics (DLGDs). DLGDs, consisting of parylene C as the upper layer and F as the lower layer, are designed to simultaneously provide good interface and bulk gate dielectric properties by exploiting the advantages of each gate dielectric. The structural effects of DLGDs are systematically investigated by evaluating the electrical characteristics and dielectric properties while varying the thickness ratio of each gate dielectric. The OFET with the optimized DLGD exhibits high performance and operational stability. This systematic approach will be useful for realizing practical electronic applications.
View details for DOI 10.1021/acsami.8b12663
View details for Web of Science ID 000449887600001
View details for PubMedID 30358384
- Fabrication of ultrathin low-voltage-driven printed organic circuits with anodized gate islands ORGANIC ELECTRONICS 2018; 62: 77–81
Pressure/Temperature Sensing Bimodal Electronic Skin with Stimulus Discriminability and Linear Sensitivity
2018; 30 (43): e1803388
Human skin imperfectly discriminates between pressure and temperature stimuli under mixed stimulation, and exhibits nonlinear sensitivity to each stimulus. Despite great advances in the field of electronic skin (E-skin), the limitations of human skin have not previously been overcome. For the first time, the development of a stimulus-discriminating and linearly sensitive bimodal E-skin that can simultaneously detect and discriminate pressure and temperature stimuli in real time is reported. By introducing a novel device design and using a temperature-independent material, near-perfect stimulus discriminability is realized. In addition, the hierarchical contact behavior of the surface-wrinkled microstructure and the optimally reduced graphene oxide in the E-skin contribute to linear sensitivity to applied pressure/temperature stimuli over wide intensity range. The E-skin exhibits a linear and high pressure sensitivity of 0.7 kPa-1 up to 25 kPa. Its operation is also robust and exhibits fast response to pressure stimulus within 50 ms. In the case of temperature stimulus, the E-skin shows a linear and reproducible temperature coefficient of resistance of 0.83% K-1 in the temperature range 22-70 °C and fast response to temperature change within 100 ms. In addition, two types of stimuli are simultaneously detected and discriminated in real time by only impedance measurements.
View details for DOI 10.1002/adma.201803388
View details for Web of Science ID 000448786000018
View details for PubMedID 30216564
Control of Concentration of Nonhydrogen-Bonded Hydroxyl Groups in Polymer Dielectrics for Organic Field-Effect Transistors with Operational Stability
ACS APPLIED MATERIALS & INTERFACES
2018; 10 (28): 24055–63
Poly(4-vinylphenol) (PVP) is a promising gate dielectric material for organic field-effect transistors (OFETs) and circuits fabricated on plastic substrates. Thermal cross-linking of PVP with a cross-linker, such as poly(melamine- co-formaldehyde) methylated (PMF), at a high temperature (above 170 °C) is widely considered an effective method to remove residual hydroxyl groups that induce polarization effects in the dielectric bulk. However, the threshold voltage shift in transfer characteristics is still observed for an OFET with a PVP-PMF dielectric when it is operated at a slow gate voltage sweep rate. The present study examines the cause of the undesired hysteresis phenomenon and suggests a route to enable a reliable operation. We systematically investigate the effect of the PVP-PMF weight ratio and their annealing temperature on the transfer characteristics of OFETs. We discover that the size of the hysteresis is closely related to the concentration of nonhydrogen-bonded hydroxyl groups in the dielectric bulk and this is controlled by the weight ratio. At a ratio of 0.5:1, a complete elimination of hysteresis was observed irrespective of the annealing temperature. We finally demonstrate a highly reliable operation of small-molecule-based OFETs fabricated on a plastic substrate at a low temperature.
View details for DOI 10.1021/acsami.8b06653
View details for Web of Science ID 000439528400070
View details for PubMedID 29938485
Printed 5-V organic operational amplifiers for various signal processing
2018; 8: 8980
The important concept of printable functional materials is about to cause a paradigm shift that we will be able to fabricate electronic devices by printing methods in air at room temperature. One of the promising applications of the printed electronics is a disposable electronic patch sensing system which can monitor the health conditions without any restraint. Operational amplifiers (OPAs) are an essential component for such sensing system, since an OPA enables a wide variety of signal processing. Here we demonstrate printed OPAs based on complementary organic semiconductor technology. They can be operated with a standard safe power source of 5 V with a minimal power consumption of 150 nW, and used as amplifiers, a variety of mathematical operators, signal converters, and oscillators. The printed micropower organic OPAs with the low voltage operation and the high versatility will open up the disposable electronic patch sensing system in near future.
View details for DOI 10.1038/s41598-018-27205-7
View details for Web of Science ID 000434920800024
View details for PubMedID 29895859
View details for PubMedCentralID PMC5997680
Freeform micropatterning of living cells into cell culture medium using direct inkjet printing
2017; 7: 14610
Microfabrication methods have widely been used to control the local cellular environment on a micron scale. However, accurately mimicking the complexity of the in vivo tissue architecture while maintaining the freedom of form and design is still a challenge when co-culturing multiple types of cells on the same substrate. For the first time, we present a drop-on-demand inkjet printing method to directly pattern living cells into a cell-friendly liquid environment. High-resolution control of cell location is achieved by precisely optimizing printing parameters with high-speed imaging of cell jetting and impacting behaviors. We demonstrated the capabilities of the direct cell printing method by co-printing different cells into various designs, including complex gradient arrangements. Finally, we applied this technique to investigate the influence of the heterogeneity and geometry of the cell population on the infectivity of seasonal H1N1 influenza virus (PR8) by generating A549 and HeLa cells printed in checkboard patterns of different sizes in a medium-filled culture dish. Direct inkjet cell patterning can be a powerful and versatile tool for both fundamental biology and applied biotechnology.
View details for DOI 10.1038/s41598-017-14726-w
View details for Web of Science ID 000414416200016
View details for PubMedID 29097768
View details for PubMedCentralID PMC5668285
- Low-Temperature, Solution-Processed, 3-D Complementary Organic FETs on Flexible Substrate IEEE TRANSACTIONS ON ELECTRON DEVICES 2017; 64 (5): 1955–59
Three-Dimensional, Inkjet-Printed Organic Transistors and Integrated Circuits with 100% Yield, High Uniformity, and Long-Term Stability
2016; 10 (11): 10324–30
In this paper, we demonstrate three-dimensional (3D) integrated circuits (ICs) based on a 3D complementary organic field-effect transistor (3D-COFET). The transistor-on-transistor structure was achieved by vertically stacking a p-type OFET over an n-type OFET with a shared gate joining the two transistors, effectively halving the footprint of printed transistors. All the functional layers including organic semiconductors, source/drain/gate electrodes, and interconnection paths were fully inkjet-printed except a parylene dielectric which was deposited by chemical vapor deposition. An array of printed 3D-COFETs and their inverter logic gates comprising over 100 transistors showed 100% yield, and the uniformity and long-term stability of the device were also investigated. A full-adder circuit, the most basic computing unit, has been successfully demonstrated using nine NAND gates based on the 3D structure. The present study fulfills the essential requirements for the fabrication of organic printed complex ICs (increased transistor density, 100% yield, high uniformity, and long-term stability), and the findings can be applied to realize more complex digital/analogue ICs and intelligent devices.
View details for DOI 10.1021/acsnano.6b06041
View details for Web of Science ID 000388913100062
View details for PubMedID 27786453
- Vertically Stacked Complementary Organic Field-Effect Transistors and Logic Circuits Fabricated by Inkjet Printing ADVANCED ELECTRONIC MATERIALS 2016; 2 (7)
- Double-shot inkjet printing for high-conductivity polymer electrode THIN SOLID FILMS 2016; 607: 55–58
Solution-Processed Vertically Stacked Complementary Organic Circuits with Inkjet-Printed Routing
2016; 3 (5): 1500439
The fabrication and measurements of solution-processed vertically stacked complementary organic field-effect transistors (FETs) with a high static noise margin (SNM) are reported. In the device structure, a bottom-gate p-type organic FET (PFET) is vertically integrated on a top-gate n-type organic FET (NFET) with the gate shared in-between. A new strategy has been proposed to maximize the SNM by matching the driving strengths of the PFET and the NFET by independently adjusting the dielectric capacitance of each type of transistor. Using ideally balanced inverters with the transistor-on-transistor structure, the first examples of universal logic gates by inkjet-printed routing are demonstrated. It is believed that this work can be extended to large-scale complementary integrated circuits with a high transistor density, simpler routing path, and high yield.
View details for DOI 10.1002/advs.201500439
View details for Web of Science ID 000377783100007
View details for PubMedID 27812468
View details for PubMedCentralID PMC5067658