Dohan Lee

Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges

We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer (50 MHz⩽M⩽13.5 GHz), we measured the S (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range (50 MHz∼1.5 GHz). The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured S parameters.

Organic based flexible speaker through enhanced conductivity of PEDOT/PSS with various solvents

Flexible organic film speaker (FOFS) was fabricated with ion assisted reaction (IAR) treated poly (vinylidene fluoide) (PVDF) as active layer and poly (3,4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT/PSS), indium tin oxide (ITO) and Cu as electrodes DC conductivity (σ DC ) of pristine PEDOT/PSS increases from 0.8 to 80 S/cm with adding various organic solvents [dimethyl sulfoxide (DMSO), N, N-dimethyl formamide (DMF), tetrahydrofuran (THF)]. The increase of σ DC of PEDOT/PSS results from screening effect of organic solvents. Frequency response of sound pressure level (SPL) of film speaker is discussed in term of total current by applied electric field. The SPL of PVDF film speaker with highly conducting PEDOT/PSS (DMSO) electrode shows more flat SPL in the frequency range from 400 Hz to 10 kHz compare to Cu or ITO electrode.

An approach to durable poly(vinylidene fluoride) thin film loudspeaker

The piezoelectric poly(vinylidene fluoride) (PVDF) surface possessing low surface energy was modified by the ion-assisted-reaction (IAR) method for the application of thin film speaker. The IAR-treated hydrophilic PVDF surface was investigated using atomic force microscopy and x-ray photoelectron spectroscopy. The adhesion strength between various types of electrodes and the film was dramatically improved due to the hydrophilic functional groups, such as -C-O-, -(C = O)-, -(C = O)-O-, and so forth. A durable loudspeaker film was fabricated by enhancing the adhesion between the screen-printed poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) and the modified PVDF films. The PVDF speaker film with the PEDOT/PSS electrode showed higher durability, flatter sound pressure level characteristics, and easier processability compared to metals or indium tin oxide electrodes.

Electrical, magnetic, and structural properties of lithium salt doped polyaniline

Abstract We report the results of temperature dependence of dc conductivity σ dc ( T ), electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) experiments for the polyaniline (PAN) doped with various lithium (Li) salts such as LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , and LiCF 3 SO 3 . A quasi one-dimensional (1D) variable range hopping (VRH) model provide the best fitting for σ dc ( T ) the Li salt doped PAN samples, which is similar to that of protonic acid (HCl) doped polyaniline samples. The σ dc and its temperature dependence vary with the kind of Li salts used. Temperature dependence of thermoelectric power of PAN doped with LiPF 6 shows the metallic behavior. From EPR experiments, we obtain that χ P depends on the kind of Li salts. The results of XPS experiments are discussed to account for the doping procedure with Li salts. Temperature dependence of EPR linewidths and X-ray diffraction patterns are compared for the various Li salt doped PAN samples. The insulator–metal transition of PAN-LiPF 6 samples is also discussed.

Study of a-Plane GaN Epitaxial Lateral Overgrowth Using Carbonized Photoresist Mask on r-Plane Sapphire

Epitaxial lateral overgrowth (ELO) a-plane GaN samples were successfully grown on masked sapphire (102) substrates using an in-situ carbonized photoresist (PR) mask by a metalorganic chemical vapor deposition (MOCVD) method. The PR masks for the ELO process were prepared using conventional lithography in the form of a stripe with an opening of 4 µm and a period of 12 µm. The stripe-patterned PR was annealed at 1100 °C in a H2 atmosphere. The stripes were aligned parallel to the GaN direction. The ELO process of GaN was strongly dependent on the direction of the stripes. Overall, the PR masks on the r-plane sapphire substrate were carbonized during the heating step before the main growth, so that the carbonized PR mask acted as an ELO mask. The study results confirmed the promising potential of the ELO process using an in-situ carbonized PR mask on r-plane sapphire.

PROPERTIES OF COPPER LAYER ON Si(100) FROM Cu(dmamb)2

Cu seed layer was deposited by chemical vapor deposition using new Cu precursor, Cu(dmamb)2. The Cu layers still need the barrier layer to prevent the diffusion, so Ta and Ti were used for the barrier layer on Si(100). Low temperature (LT) copper buffer layer was introduced and the effect of the buffer on the Cu films was investigated. The grown Cu layers were analyzed using FESEM, XRD, and four point probe measurement. The Cu seed layers were successfully deposited using Cu(dmamb)2 precursor. Better thickness uniformity was obtained in the Cu films with the LT Cu buffer, which lowered the electrical resistivity.