Mari Koizumi

Ultraflexible organic photonic skin

Optoelectronic electronic skins, or e-skins, introduce electronic sensing and displays on the surface of human skin. Thin-film electronics intimately laminated onto the skin imperceptibly equip the human body with electronic components for health-monitoring and information technologies. When electronic devices are worn, the mechanical flexibility and/or stretchability of thin-film devices helps to minimize the stress and discomfort associated with wear because of their conformability and softness. For industrial applications, it is important to fabricate wearable devices using processing methods that maximize throughput and minimize cost. We demonstrate ultraflexible and conformable three-color, highly efficient polymer light-emitting diodes (PLEDs) and organic photodetectors (OPDs) to realize optoelectronic skins (oe-skins) that introduce multiple electronic functionalities such as sensing and displays on the surface of human skin. The total thickness of the devices, including the substrate and encapsulation layer, is only 3 μm, which is one order of magnitude thinner than the epidermal layer of human skin. By integrating green and red PLEDs with OPDs, we fabricate an ultraflexible reflective pulse oximeter. The device unobtrusively measures the oxygen concentration of blood when laminated on a finger. On-skin seven-segment digital displays and color indicators can visualize data directly on the body.

30.3 Organic-transistor-based 2kV ESD-tolerant flexible wet sensor sheet for biomedical applications with wireless power and data transmission using 13.56MHz magnetic resonance

A wet sensor, which detects the presence or absence of liquid, is an important tool for biomedical, nursing-care, and elderly-care applications such as the detection of blood in bandages, sweat in underwear, and urination in diapers. A wet sensor should be a thin, mechanically flexible, large-area, and low-cost device with wireless power and data transmission, because constant monitoring with a rigid and wired wet sensor placed on human skin is annoying. Moreover, the wet sensor should be disposable from a hygiene perspective. In order to meet these requirements, an organic transistor based flexible wet sensor sheet (FWSS) with wireless power and data transmission using 13.56MHz magnetic resonance is developed to detect urination in diapers.

Dual-gate organic phototransistor with high-gain and linear photoresponse

The conversion of light into electrical signal in a photodetector is a crucial process for a wide range of technological applications. Here we report a new device concept of dual-gate phototransistor that combines the operation of photodiodes and phototransistors to simultaneously enable high-gain and linear photoresponse without requiring external circuitry. In an oppositely biased, dual-gate transistor based on a solution-processed organic heterojunction layer, we find that the presence of both n- and p-type channels enables both photogenerated electrons and holes to efficiently separate and transport in the same semiconducting layer. This operation enables effective control of trap carrier density that leads to linear photoresponse with high photoconductive gain and a significant reduction of electrical noise. As we demonstrate using a large-area, 8 × 8 imaging array of dual-gate phototransistors, this device concept is promising for high-performance and scalable photodetectors with tunable dynamic range.High-resolution imaging technologies call for photodetectors with high-gain and linear response over a large dynamic range. Chow et al. show a dual-gate structure that combines the operation of photodiodes and phototransistors to enable both amplified and linear response without external circuitry.

Ultrathin, short channel, thermally-stable organic transistors for neural interface systems

We present here design and fabrication of short channel organic thin film transistor with uniform performance and good thermal stability for utilization in neural interface systems. Transistors are fabricated on ultra-thin parylene diX-SR substrate which provides great flexibility and conformability to curvilinear surfaces. With channel length as short as 2μm, transistors show low contact resistance and good mobility in bottom contact architecture for higher operating frequencies. As a crucial factor for sterilization, our transistors demonstrate excellent thermal stability and remain functional up to 170°C. The low operating voltage and their heat durability prospect those devices to serve as an efficient interface to the complex texture of brain tissue for future applications.