Hongki Kang

Using a novel high-speed, femtoliter-scale, micro-gravure printing with unprecedented scaling to the sub-10 μm regime and appropriately formulated, characterized, and optimized nanoparticle and polymer ink materials, highly scaled organic thin-film-transistors (OTFTs) are realized. They have excellent DC and AC characteristics and achieve record transition frequencies of 300 kHz, which opens up new classes of applications. Detailed facts of importance to specialist readers are published as ”Supp

Inkjet printing of thermoplasmonic nanoparticles enables instantaneous, large-area heat pattern generation upon light illumination from distance. By printing multiple metal nanoparticles of different shapes overlaid, we can fabricate multiwavelength thermoplasmonic images, which generate different heat patterns from a single printed image depending on the wavelength choice of light. In this work, we propose a novel multiwavelength thermoplasmonic image printing process that can be used for antic

Localized heat generation by the thermo-plasmonic effect of metal nanoparticles has great potential in biomedical engineering research. Precise patterning of the nanoparticles using inkjet printing can enable the application of the thermo-plasmonic effect in a well-controlled way (shape and intensity). However, a universally applicable inkjet printing process that allows good control in patterning and assembly of nanoparticles with good biocompatibility is missing. Here we developed inkjet-print

In this work, we study the optimization of the geometry of inkjet-printed polymer films and develop a simple analytic framework to understand our results and establish limitations on inkjet-printed patterns. We show how drop spacing and ink concentration affect the thickness of a printed film and how hydrostatic conditions with contact angle hysteresis have to be considered to print optimized rectangular features. If advancing and receding contact angle are not taken into account, printed featur

An analytical threshold voltage model for double-gate MOSFETs with localized charges is developed. From the 2-D Poisson's equation with parabolic potential approximation, a compact threshold voltage model is derived. The proposed model is then verified with a 2-D device simulator. The model can be used to investigate hot-carrier-induced device degradation for various device dimensions and various charge distributions.

Thermoplasmonic effect-based neural stimulation has been suggested as an alternative optical neural stimulation technology without genetic modification. Integration of near-infrared light with plasmonic gold nanoparticles has been demonstrated as a neuromodulation tool on <i>in vitro</i> neuronal network models. In order to further test the validity of the thermoplasmonic neural stimulation across multiple biological models (<i>in vitro</i>, <i>ex vivo</i>, and <i>in vivo</i>) avoiding genetic m

In order to facilitate accurate noise modeling of organic thin-film-transistors (OTFTs), we provide comprehensive experimental results and analysis of unique low frequency noise characteristics in OTFTs. We conduct drain current noise measurements for pentacene-based thin-film-transistors (TFTs) having different grain size and operating region and use the resulting data to provide detailed mechanistic understanding of the underlying noise-generation phenomena that exist in OTFTs. The results sho

We propose inkjet-printed high-speed and transparent temperature sensors based on the thermoelectric effect for direct monitoring of the photothermal effect. They consist of highly transparent organic thermoelectric materials that allow excellent biocompatibility and sub-ms temporal resolution, simultaneously. Our transparent thermoelectric temperature sensors can be used to advance various photothermal biomedical applications.

Abstract Electro‐optical neural interface technologies provide great potential and versatility in neuroscience research. High temporal resolution of electrical neural recording and high spatial resolution of optical neural interfacing such as calcium imaging or optogenetics complimentarily benefit the way information is accessed from neuronal networks. To develop a hybrid neural interface platform, it is necessary to build transparent, soft, flexible microelectrode arrays (MEAs) capable of measu

Recently, interest in transparent electrodes has been increasing in biomedical engineering applications for such as electro-optical hybrid neuro-technologies. However, conventional photolithography-based electrode fabrication methods have limited design customization and large-area applicability. For biomedical engineering applications, it is crucial that we can easily customize the electrode design for different patients over a large body area. In this paper, we propose a novel method to fabric

An understanding of 1/f noise in organic thin film transistors (OTFTs) is critical to their deployment in a range of analog and mixed signal applications. In particular, an understanding of 1/f noise behavior during switching is vital and has not been reported to date. Here, we conduct drain current noise measurements for polymer based OTFTs while the OTFT switch between accumulation mode and depletion mode. The results show that capture and emission of the carriers by/from traps within the semi

Stretchable strain sensors have been proposed for personalized healthcare monitoring or human motion detection in a skin-mountable form factor. For customization and stretchable substrate-compatible low-temperature processing, various printing technologies have been utilized to fabricate strain sensors. Hydrophobic stretchable polymers and low viscosity conductive inks are typically used in printed high resolution strain sensor fabrications. However, directly printed strain sensors on hydrophobi

Photothermal neuromodulation is a promising non-electrical neural stimulation technology for treating brain diseases through optically induced cell membrane temperature changes. However, the technology faces limitations in understanding its mechanism and impact on cellular behavior due to the restriction of directly measuring temperature changes at the cell interface from a very close distance during optical stimulation of neural cells, necessitating advancements in high-precision temperature se