1. Flexible Integrated Circuit System

■ Research Purpose

  • To fabricate flexible 3D integrated circuits by using inkjet printing process.

■ Research Contents

  • Organic field-effect transistors (OFETs) have been proposed for various applications. Circuits and systems requires no static power dissipation, wide noise margins, and high operational performance stability against transistor parameter variations. In silicon-based integrated circuits, these requirements were achieved by using complementary (both p- and n-type) transistors.

(a) Conventional complementary transistors vs. 3D-stacked complementary transistors.

b) Schematic cross-section of the 3D complementary OFETs.

   The same approach was adopted for the implementation of organic complementary circuits. However, all these circuits have been based on two-dimensional planar structures with p-type OFET (PFET) and n-type OFET (NFET) fabricated on the same floor. Instead, we have adopted the 3D integration of complementary OFETs to overcome the physical limits of two-dimensional integration. Based on this 3D integration, we are currently fabricating various organic circuits on plastic substrates with high transistor density.

(A flexible integrated circuits on plastic substrate)

   Also, we are focusing on the development of robust, high yield, and predictable fabrication process of flexible organic integrated circuits based on inkjet printing technique that is applicable to low cost roll-to-roll process. The complex printed electronic systems can be designed and fabricated based on this process including customized design rule, device model, and optimized process conditions.

2. Flexible Solar cell & OLED

■ Research Purpose

  • To develop OLEDs driven by OPV power, series/parallel connected OPV device design and high-efficient OLEDs by preferentially horizontal plane-on orientation

​■ Research Contents

  • Organic light emitting diodes (OLEDs) have potential applications in next-generation electronics due to advantages such as low driving voltage, wide view-angle, self-emitting property, and applicability to flexible large-area display and lighting.                                                            

(Molecular orientation for highly-efficient OLEDs / Org. Elec. 24 (2015) 234)

(Flexible OPV)

     To improve device efficiency, functional organic materials are required because high efficient charge injection and transport into OLEDs are the limiting factors in determine operating voltage and device efficiency. We have focused on determining the molecular orientation change according to substituent position of anthracene core in a new anthracene derivative that is intended for use as a non-doped emitter. To accomplish this quantization we used two-dimensional GIXD (2D-GIXD) analysis. OLEDs with BDNPA non-doped emitter showed higher current efficiency by more than a factor of five compare to the vertical orientation due to the carrier mobility with well-aligned π-stacking structure toward out-of-plane by the horizontal orientation.

3. Wearable Biosensors

■ Research Purpose

  • To develop wearable, low-cost biosensors that can reach real-world health care market.

■ Research Contents

  • Organic field-effect transistor(OFET) possess attractive properties such as mechanical flexibility, printability, and low manufacturing costs. Biosensors based OFET, therefore, can be fabricated on flexible substrates which makes themselves wearable sensors, and manufacturing cost is relatively low. For these reasons, they have gradually gained attention for their potential applications as low-cost, disposable, wearable sensors.

  • Extended-gate type OFET-based biochemical sensor for lactate detection

(Schematic illustration of the extended-gate type OFET sensor for lactate detection)

   One example is a wearable biochemical sensor for lactate detection. Lactate is included in human sweat and it is a biomarker for exercise status of athletes, clinical diagnosis, and freshness of food. Enzyme-functionalized electrode composes biofuel cell with Ag/AgCl reference electrode in aqueous media. As the concentration of lactate increases, the enzymatic redox chain reaction of lactate causes potential difference between the two electrodes in the biofuel cell which results in threshold voltage shift in an OFET. This kind of biosensor possess potential for practical wearable lactate sensors.

  • OFET-based biosensors have showed great potentials but they are still in their early stages of development. Many of the current sensors are at research level. Therefore, Our lab. pursue a goal of developing OFET-based biosensors systemically to carry them close to real-world health care market.