Sung Hun Jin

Multifunctional Epidermal Electronics Printed Directly Onto the Skin

Materials and designs are presented for electronics and sensors that can be conformally and robustly integrated onto the surface of the skin. A multifunctional device of this type can record various physiological signals relevant to health and wellness. This class of technology offers capabilities in biocompatible, non-invasive measurement that lie beyond those available with conventional, point-contact electrode interfaces to the skin.

Microstructured elastomeric surfaces with reversible adhesion and examples of their use in deterministic assembly by transfer printing

Reversible control of adhesion is an important feature of many desired, existing, and potential systems, including climbing robots, medical tapes, and stamps for transfer printing. We present experimental and theoretical studies of pressure modulated adhesion between flat, stiff objects and elastomeric surfaces with sharp features of surface relief in optimized geometries. Here, the strength of nonspecific adhesion can be switched by more than three orders of magnitude, from strong to weak, in a reversible fashion. Implementing these concepts in advanced stamps for transfer printing enables versatile modes for deterministic assembly of solid materials in micro/nanostructured forms. Demonstrations in printed two- and three-dimensional collections of silicon platelets and membranes illustrate some capabilities. An unusual type of transistor that incorporates a printed gate electrode, an air gap dielectric, and an aligned array of single walled carbon nanotubes provides a device example.

Using nanoscale thermocapillary flows to create arrays of purely semiconducting single-walled carbon nanotubes

Among the remarkable variety of semiconducting nanomaterials that have been discovered over the past two decades, single-walled carbon nanotubes remain uniquely well suited for applications in high-performance electronics, sensors and other technologies. The most advanced opportunities demand the ability to form perfectly aligned, horizontal arrays of purely semiconducting, chemically pristine carbon nanotubes. Here, we present strategies that offer this capability. Nanoscale thermocapillary flows in thin-film organic coatings followed by reactive ion etching serve as highly efficient means for selectively removing metallic carbon nanotubes from electronically heterogeneous aligned arrays grown on quartz substrates. The low temperatures and unusual physics associated with this process enable robust, scalable operation, with clear potential for practical use. We carry out detailed experimental and theoretical studies to reveal all of the essential attributes of the underlying thermophysical phenomena. We demonstrate use of the purified arrays in transistors that achieve mobilities exceeding 1,000 cm(2) V(-1) s(-1) and on/off switching ratios of ∼10,000 with current outputs in the milliamp range. Simple logic gates built using such devices represent the first steps toward integration into more complex circuits.

Hysteresis mechanism and reduction method in the bottom-contact pentacene thin-film transistors with cross-linked poly(vinyl alcohol) gate insulator

The origin of the hysteresis phenomenon in bottom-contact pentacene organic thin-film transistors (OTFTs) with cross-linked poly(vinyl alcohol) (PVA) insulator is studied. From electrical measurements with various sweep ranges and two different sweep directions, the hysteresis effect is presumed to be caused by the electrons or holes that could be injected from the gate and trapped in the PVA bulk, rather than by the polarization or internally existing mobile ions. The assumption is confirmed by the clear reduction of hysteresis in OTFTs with a blocking oxide layer between gate and PVA insulator.

Deterministic assembly of releasable single crystal silicon-metal oxide field-effect devices formed from bulk wafers

Deterministic assembly of ultrathin metal oxide-semiconductor field-effect transistors released from the surfaces of bulk wafers with (111) orientation provides a route to high quality electronics on nearly any type of substrate. Device parameters and bias stability characteristics from transistors on sheets of plastic confirm the effectiveness of the approach and the critical roles of thermally grown layers of silicon dioxide for the gate dielectrics and passivation layers. Systematic studies of the anisotropic etching processes used to release the devices illustrate capabilities into the sub-micron thickness regime, with beneficial effects on the bending stiffness and degree of bendability.

Water-Soluble Thin Film Transistors and Circuits Based on Amorphous Indium–Gallium–Zinc Oxide

This paper presents device designs, circuit demonstrations, and dissolution kinetics for amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) comprised completely of water-soluble materials, including SiNx, SiOx, molybdenum, and poly(vinyl alcohol) (PVA). Collections of these types of physically transient a-IGZO TFTs and 5-stage ring oscillators (ROs), constructed with them, show field effect mobilities (∼10 cm2/Vs), on/off ratios (∼2×10(6)), subthreshold slopes (∼220 mV/dec), Ohmic contact properties, and oscillation frequency of 5.67 kHz at supply voltages of 19 V, all comparable to otherwise similar devices constructed in conventional ways with standard, nontransient materials. Studies of dissolution kinetics for a-IGZO films in deionized water, bovine serum, and phosphate buffer saline solution provide data of relevance for the potential use of these materials and this technology in temporary biomedical implants.

Solution-processed single-walled carbon nanotube field effect transistors and bootstrapped inverters for disintegratable, transient electronics

This paper presents materials, device designs, and physical/electrical characteristics of a form of nanotube electronics that is physically transient, in the sense that all constituent elements dissolve and/or disperse upon immersion into water. Studies of contact effects illustrate the ability to use water soluble metals such as magnesium for source/drain contacts in nanotube based field effect transistors. High mobilities and on/off ratios in transistors that use molybdenum, silicon nitride, and silicon oxide enable full swing characteristics for inverters at low voltages (∼5 V) and with high gains (∼30). Dissolution/disintegration tests of such systems on water soluble sheets of polyvinyl alcohol demonstrate physical transience within 30 min.

Microwave purification of large-area horizontally aligned arrays of single-walled carbon nanotubes

Recent progress in the field of single-walled carbon nanotubes (SWNTs) significantly enhances the potential for practical use of this remarkable class of material in advanced electronic and sensor devices. One of the most daunting challenges is in creating large-area, perfectly aligned arrays of purely semiconducting SWNTs (s-SWNTs). Here we introduce a simple, scalable, large-area scheme that achieves this goal through microwave irradiation of aligned SWNTs grown on quartz substrates. Microstrip dipole antennas of low work-function metals concentrate the microwaves and selectively couple them into only the metallic SWNTs (m-SWNTs). The result allows for complete removal of all m-SWNTs, as revealed through systematic experimental and computational studies of the process. As one demonstration of the effectiveness, implementing this method on large arrays consisting of ~20,000 SWNTs completely removes all of the m-SWNTs (~7,000) to yield a purity of s-SWNTs that corresponds, quantitatively, to at least to 99.9925% and likely significantly higher.

Improvement of Long-Term Durability and Bias Stress Stability in p-Type SnO Thin-Film Transistors Using a SU-8 Passivation Layer

We investigate the effects of ambient atmosphere on the electrical performance of p-type tin monoxide (SnO) thin-film transistors (TFTs), and present the effective method for the passivation of SnO TFTs using a SU-8 organic layer. The experimental data shows that the SnO TFTs without a passivation layer suffer from the electrical performance degradation under humid environments, which implies that the formation of the passivation layer is necessary in p-type SnO TFTs for the stable operation of the devices. The SU-8 organic layer was successfully incorporated as a passivation layer of SnO TFTs. The SnO TFTs with a SU-8 passivation layer exhibit very similar transfer characteristics with those without a passivation layer, and show much improved long-term durability and bias stress stability compared with the SnO TFTs without a passivation layer under air environments.

Effect of variations in diameter and density on the statistics of aligned array carbon-nanotube field effect transistors

This paper describes a systematic experimental and theoretical analysis of performance variations in transistors that use aligned arrays of single-wall carbon nanotubes (SWNTs) grown on quartz substrates. Theoretical models, calibrated using measurements on statistically relevant numbers of transistors that each incorporate an individual aligned semiconducting SWNT, enable separate examination of different contributors to measured variations in transistors that incorporate arrays of SWNTs. Using these models and associated experiments, we study the scaling of the statistics of key performance attributes in transistors with different numbers of incorporated SWNTs and reveal long-range spatial nonuniformities in the distributions of SWNT diameters as the main contributor to observed performance variability.