Jinho Bae

Organic diode with high rectification ratio made of electrohydrodynamic printed organic layers

In this paper, an all-printed organic diode to reveal a high rectification ratio (∼1.2 × 104) is proposed using organic heterojunction materials N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine (TPD) and fullerene (C60). The proposed organic diode is fabricated as a structure of ITO/TPD/C60/Al on a glass substrate through an all-printed electrohydrodynamic (EHD) technique, which has an effective area of 2 × 2 mm2. The threshold voltage of the forward bias is 1.2 V and the current density reaches 550 mA/cm2 at 3 V. The device is characterized by current voltage I-V at temperature 30°C to 120°C, and junction capacitance is analyzed at 4 kHz frequency at ±2 V. To verify the successful construction of all layers deposited through the EHD technique, morphology analysis was carried out with FE-SEM. From these measured electrical characteristics, suitability for rectification purposes in printed electronics is confirmed.

Stretchable photo sensor using perylene/graphene composite on ridged polydimethylsiloxane substrate.

To apply in wearable electronics, we propose a stretchable photo sensor that detects an inversely changed resistance by varying light intensity, which is stably operated up to 25% axial strain. Especially, the stretchabity of the proposed photo sensor is achived by using a uniform ridged substrate made of polydimethylsiloxane (PDMS). The proposed device is composed of a thin film of perylene/graphene composite, which is sandwiched between bottom and top indium tin oxide (ITO) transparent electrodes fabricated through electro-hydrodynamic (EHD) technique. The electrical conductivity of perylene is improved by blending graphene with it. The resistance of the proposed photo sensor changes from 108 MΩ to 87 MΩ within the light intensity range of 0 to 400 lux, respectively. Furthermore, the flexibility is verified through a bendability test from 16 mm down to 0 mm and a bending endurance test for more than 1000 cycles. Uniform and smooth deposition of the active layer is tested through surface morphology characterization.

Microstrip Patch Sensor for Salinity Determination

In this paper, a compact microstrip feed inset patch sensor is proposed for measuring the salinities in seawater. The working principle of the proposed sensor depends on the fact that different salinities in liquid have different relative permittivities and cause different resonance frequencies. The proposed sensor can obtain better sensitivity to salinity changes than common sensors using conductivity change, since the relative permittivity change to salinity is 2.5 times more sensitive than the conductivity change. The patch and ground plane of the proposed sensor are fabricated by conductive copper spray coating on the masks made by 3D printer. The fabricated patch and the ground plane are bonded to a commercial silicon substrate and then attached to 5 mm-high chamber made by 3D printer so that it contains only 1 mL seawater. For easy fabrication and testing, the maximum resonance frequency was selected under 3 GHz and to cover salinities in real seawater, it was assumed that the salinity changes from 20 to 35 ppt. The sensor was designed by the finite element method-based ANSYS high-frequency structure simulator (HFSS), and it can detect the salinity with 0.01 ppt resolution. The designed sensor has a resonance frequency separation of 37.9 kHz and reflection coefficients under −20 dB at the resonant frequencies. The fabricated sensor showed better performance with average frequency separation of 48 kHz and maximum reflection coefficient of −35 dB. By comparing with the existing sensors, the proposed compact and low-cost sensor showed a better detection capability. Therefore, the proposed patch sensor can be utilized in radio frequency (RF) tunable sensors for salinity determination.

Resistive switching device with highly-asymmetric current-voltage characteristics: A solution to backward sneak current in passive crossbar arrays

With the view towards future non-volatile random access memories that can be integrated at a large scale, extensive study on resistive switching (RS) devices arranged in a crossbar array is currently underway. Although the crossbar array architecture offers relatively simple and acceptable scalability, the presence of sneak current is recognized as a critical issue that needs to be resolved at device level. In addressing this issue, we demonstrate a new type of RS device fabricated by combining graphene oxide (G-O) and zinc oxide (ZnO) with highly asymmetric current-voltage (I-V) characteristics depending on the polarity of bias voltage. The distinctive highly asymmetric I-V characteristics result from the presence of a hetero-junction interface formed between the G-O and ZnO layers. This hetero-junction manifests resistance in the range of GΩ under both forward and reverse bias voltage when the device is in the OFF state, in contrast, when the device is in the ON state, it exhibits resistance in the range of MΩ or kΩ under forward bias and GΩ under reverse bias. We propose to employ demonstrated RS devices with highly asymmetric I-V characteristics to mitigate adverse effects of the sneak current.

Target Path Detection Algorithm Using Activation Time Lag of PDR Sensors Based on USN

Abstract This paper proposes the target path detection algorithm using statistical characteristics of an activated time lag along a moving path of target from a neighboring sensor in PDR(Pulse Doppler Radar) sensor node environment based on USN(Ubiquitous Sensor Network) with a limitation detecting only an existence of moving target. In the proposed algorithm, detection and non-detection time lag obtained from the experimental data are used. The experimental data are through repetitive action of each 500 times about three path scenarios such as passing in between two sensors, moving parallel to two sensors, and turning through two sensors. From this experiments, error detection percentages of three path scenarios are 5.67%, 5.83%, and 7.17%, respectively. They show that the proposed algorithm can exactly detect a target path using the limited PDR sensor nodes. Key Words : Pulse Doppler Radar, Path Detection Algorithm, Unattended Ground Sensor, USN, NCW Ⅰ. 서 론 현대전은 네트워크 중심전(NCW: Network Centric Warfare) 체계로 발전하고 있다. 탐지, 지휘, 타격 체계 등 여러 전투 요소를 통신 체계로 연계하여 정보의 우월성 확보로 지휘속도 향상, 신속한 작전 전개, 치명적 타격, 생존성 향상 등 전투력을 극대화 시키는 작전수행 개념이다.

Flexible and stackable non-volatile resistive memory for high integration

We propose a novel flexible and stackable resistive random access memory (ReRAM) array with multi-layered crossbar structures fabricated on a PET flexible substrate through EHD system. The basic memory block of the proposed device is based on one resistor and multi-layered column memristors (1R-MCM) structure, which can be easily extended to 3 dimensional columns for a high integration. To fabricate the device, the materials Ag for top and bottom electrodes, PVP for memristor, and (MEH:PPV and PMMA in acetonitrile) for pull-up resistors are used. Memory single cell is consisted of a high OFF/ON ratio (~4663) memristor and a pull-up resistor (20 MΩ) that operate on the principles of voltage divider circuit. Memory logic data is retrieve in the form of voltage levels instead of sensing current the of crossbar array. Two memory crossbar arrays are stacked vertically and they are sharing column bars, each column’s memristors are with a single pull-up resistor. A 3x3 stacked memory with two layers that can store 18 bits of data is demonstrated to realize on a small area for a high integration.

Stretchable photo sensor based on graphene/perylene composite utilizing electrohydrodynamic fabrication technique

We propose a stretchable photo sensor fabricated on uniform ridged polydimethylsiloxane PDMS substrate through electro-hydrodynamic (EHD) technique. An active layer, perylene/graphene composite thin film (67nm) is sandwiched between top and bottom ITO electrodes. The electrical conductivity of the perylene is enhanced by blending with graphene. The photo sensor changes the terminal resistance from 108MΩ to 87MΩ against light intensity of 0~400lux, respectively. To verify a stretchability, the proposed photo sensor under mechanical strain of 25% is normally worked, and it is stretchable up to 50% strain, maximally. A mechanical bendability test is carried out by folding the device for 1000 endurance cycles, while there is no change in the electrical behavior.

Digital beamsteering system using acoustic transducer array.

Acoustic signal processing can be applied to sonar, acoustic communications and multimedia applications. Especially transmitting acoustic signal to the desired direction has many applications in military and industry. In this paper, we present digital beamsteering algorithm using parametric array transducers. To generate the desired beampattern, the proposed algorithm utilizes the complex weight instead of time delay. With this complex operation, many algorithms including constant beamwidth algorithm and linear constrained beamforming algorithms can be applied to make versatile transmitting beampatterns. To verify the generated beampattern, we build acoustic beamsteering system by using commercial transducers and LABVIEW software and hardware. The system includes GUI software, which allows user to change many parameters such as number of sensors, complex weight of each sensor, type of transmit data, etc. The GUI can also be easily modified and extended to accommodate the characteristics of transducers. Wi...

Disposable all-printed electronic biosensor for instantaneous detection and classification of pathogens

A novel disposable all-printed electronic biosensor is proposed for a fast detection and classification of bacteria. This biosensor is applied to classify three types of popular pathogens: Salmonella typhimurium, and the Escherichia coli strains JM109 and DH5-α. The proposed sensor consists of inter-digital silver electrodes fabricated through an inkjet material printer and silver nanowires uniformly decorated on the electrodes through the electrohydrodynamic technique on a polyamide based polyethylene terephthalate substrate. The best sensitivity of the proposed sensor is achieved at 200 µm teeth spaces of the inter-digital electrodes along the density of the silver nanowires at 30 × 103/mm2. The biosensor operates on ±2.5 V and gives the impedance value against each bacteria type in 8 min after sample injection. The sample data are measured through an impedance analyzer and analyzed through pattern recognition methods such as linear discriminate analysis, maximum likelihood, and back propagation artificial neural network to classify each type of bacteria. A perfect classification and cross-validation is achieved by using the unique fingerprints extracted from the proposed biosensor through all the applied classifiers. The overall experimental results demonstrate that the proposed disposable all-printed biosensor is applicable for the rapid detection and classification of pathogens.

Memristor-capacitor passive filters to tune both cut-off frequency and bandwidth

In various optical sensor applications, programmable analog filters are desirable to reduce the hardware requirement. Memristor is two state programmable nonvolatile resistor, which has a small size and low power consumption. Using these resistance switching characteristics of a memristor, we propose a novel memristor-capacitor (MC) based printed low pass and high pass filters for analog circuits to achieve tunable cut-off frequencies and bandwidth. The cut-off frequencies of filters are controlled through a memristor state switching (HRS/LRS), whereas the capacitor has a fixed value. The proposed MC filters utilize graphene/poly 4-vinlyphenol (G/PVP) for dielectric layer of capacitors and Graphene Quatum Dots (GQDs)/PVP for an active layer of memristor, and these layers are fabricated on ITO coated flexible PET substrate through electrohydrodynamic (EHD) technique. Both MC filters are designed as parameters of two state memristance and a capacitance. From comparison between designed and fabricated filters, we show that they are matched quite well.