Seung-Min Lee

Electronics and Telecommunications Research Institute | ETRI · ICT materials research group

Thermal management is essential for living organisms and electronic devices to survive and maintain their own functions. However, developing flexible cooling devices for flexible electronics or biological systems is challenging because conventional coolers are bulky and require rigid batteries. In nature, skins help to maintain a constant body temp...

Inspired by perspiration, the first membrane‐type active cooler is presented by Seung Eon Moon and co‐workers in article number 1905901. Mechanically programmed thermoresponsive hydrogel valves efficiently expose water at high temperature and cool down the system with evaporation, whereas they cover water at low temperature to save water and therma...

To attain power generation with body heat, the thermal resistance matched design of the thermoelectric generator was the principal factor which was not critical in the case of thermoelectric generator for the waste heat generation. The dimension of thermoelectric legs and the number of thermoelectric leg-pairs dependent output power performances of...

On Si and sapphire substrates, 6–45 nm thick films of atomic layer-deposited Al\(_{2}\)O\(_{3}\) were grown. The thermal conductivity of ALD films has been determined from a linear relation between film thickness and thermal resistance measured by the 3\(\omega \) method. ALD films on Si and sapphire showed almost same thermal conductivity in the t...

An electrical resistivity evaluation method for a pillar-shaped solid material, especially a brittle thermoelectric Bi2Te3, is presented with short compensation based on a probing apparatus with four-spring pins. The method eliminates the process of modelling a complex contact resistance, resulting in a simple but reproducible characterisation with...

A micro-electro-mechanical-system (MEMS)-based NO2 gas sensor was fabricated and characterized by using ZnO nano-rods for the Internet of Things (IoT) monitoring system. The implementation process was fully compatible with the standard 6-inch 0.8-μm complementary metal oxide semiconductor (CMOS) process for mass-production, resulting in the simple...

A critical challenge in using thermoelectric generators (TEGs) for charging the portable or wearable electronics has been their limited outputs, as available temperature differential on human body (∆Text) is typically less than 10 K. Furthermore, the thermal resistance (Rth) at the TEG–air interface often overwhelms Rth of TEG itself, which makes t...

Micro carbon dioxide gas sensor with low power consumption and high selectivity was fabricated based on micro-heater and electrochemical operation method. Li3PO4 thick film for solid electrolyte and Li2CO3 thick film for sensing material were deposited successively using screen printing technique on Si substrate in the form of slurry. In structure...

A new aerosol deposition method was used to fabricate thick Bi-Te based thermoelectric films, such as p-type Bi0.5Sb1.5Te3 and n-type Bi2Te2.7Se0.3. The fabricated films exhibited dense morphologies without any large-scale porosity. Measured films thicknesses of Bi0.5Sb1.5Te3 and Bi2Te2.7Se0.3 were 276 μm and 557 μm, respectively. The thermoelectri...

The thermal conductivity of atomic layer deposited (ALD) Al 2 O 3 films was measured using the 3w method in the temperature range of 50 K-320 K. The ALD films were deposited onto 0.43 mm thick sapphire (1000) sub-strates in the thickness range of 5 nm-40 nm. For the heater and thermometer , ~330 nm thick Au with ~3 nm thick adhesion layer of Ti was...

To study the electric and the thermoelectric properties of silicon thin films (SiTFs), we fabricated devices having SiTFs by using conventional complementary metal-oxide-semiconductor (CMOS)-compatible processes for mass production and extendibility. The conductivities and the Seebeck coefficients of SiTFs for dose concentrations of 5 × 1014 cm -2,...

The single crystal of the electron doped BaSnO3-δ system has been recently found to have high electrical mobility (up to 320 cm2V-1s-1) at room temperature and excellent oxygen stability. Although thermal conductivity (κ) of the BaSnO3-δ single crystal is an important physical quantity, the κ measurement by the conventional DC method has been diffi...

We have developed a procedure to measure the thermal conductivity of dielectric liquids and gases using a steady state ac hot wire method in which a thin metal wire is used as a heater and thermometer. The temperature response of the heater wire was measured in a four-probe geometry using an electronic circuit developed for the conventional 3omega...

A magnetic flux-guide in the form of a sharp needle is known to enhance the spatial resolution of the scanning SQUID microscope. We investigated the properties of a soft ferromagnetic tip as a flux-guide by measuring the local field of the tip end. The effects of the flux-guide, such as the transmission of a magnetic signal, length dependence, and...

We have constructed an NDE system using an array of four HTS SQUID sensors. The sensor array was fabricated on a SrTiO₃ bi-crystal substrate. The SQUID pickup loops were held perpendicular to the device under test. The lateral dimension of the SQUID was 20 micrometers and the noise was typically less than 30 pT/Hz¹2/ at 10 Hz....

We present experimental procedure to measure thermal boundary conductance at solid-solid interfaces based on the 3ω method. The measurements have been performed on superlattice, multilayer and composite films. Also measured is the thermal conductance between various metal films and sapphire crystal substrate. The results are discussed on the basis...

Double-sided YBa2Cu3O7-δ (YBCO) thin films were prepared on LaAlO3 substrates 50 mm in diameter by an off-axis pulsed laser deposition method. The surface of the YBCO films appeared to have low a boulder density with a surface roughness of about 3 nm. Spiral growth was observed at both sides of the thin films. X-ray diffraction data showed that the...

We have fabricated and characterized multilayer high-T_c SQUID magnetometers designed for a magnetically unshielded environment. The magnetometers consist of YBa₂Cu₃O_7-x(YBCO)/SrTiO₃(STO)/YBCO trilayers deposited by pulsed laser deposition (PLD) on an STO bi-crystal substrate. We fabricated SQU...

We have fabricated Josephson junctions by modifying ramp edges of the base electrodes without depositing any artificial barrier layer. We irradiated the ramp edge surfaces with ion beams and heat-treated them under various conditions prior to the deposition of counter-electrode layers. After patterning the samples into ramp edge junctions using pho...

The thermal conductivity of sputtered amorphous-Ge2Sb2Te5 (a-GST)/ZnS:SiO2 and crystalline-Ge2Sb2Te5 (c-GST)/ZnS:SiO2 multilayer films has been measured in the temperature range between 50 and 300 K using the 3ω method. The conductivity data in the direction of the cross plane of the films showed lower values than the series conductance of the cons...

We report the thermal conductivity of some DVD materials, amorphous/crystalline-Ge_2Sb_2Te_5(a/c-GST), ZnS:SiO2 and Al-alloy layers. Ge_2Sb_2Te5 alloy is a phase-change material proper to rewritable digital versatile disk(DVD), which is a promising storage media for multimedia application. The thermal conductivity of these sputtered films has been...

The thermal conductivity of RF sputtered ZnS:SiO2 composite film is measured in the temperature range between 50 K and 300 K using the 3ω method. This composite film shows two distinct modes of behavior. One is that, at room temperature, the thermal conductivity of the composite film is lower than the conventionally estimated minimum values for dis...

Accurate and simple measurements of the thermal conductivity of thin films deposited on high thermal conductivity substrates have been recently enabled by the development of an Ac hot-wire method, the 3 omega method. Recent progress in the measurement and understanding of heat transport in ultra-thin films (much less than 1 mu m thick) and multilay...

The thermal conductivities of sol-gel derived SrTiO 3 and CaTiO 3 polycrystalline films were measured using the 3ω method along the direction perpendicular to the film plane in the temperature range between 40 K and 300 K. The thermal conductivity data for the films showed glass-like temperature dependence that the conductivity decreased with decre...

We have fabricated a compact narrowband microstrip hairpin-comb filter for PCS applications by patterning double-sided YBCO films prepared by pulsed laser deposition on a 50-mm-diameter, 0.5-mm-thick LaAlO₃ wafer. To achieve the desired performance with the size limitation, folded half-wavelength resonators are all oriented in the same d...

The thermal conductivities of α-Al2O3 and κ-Al2O3 wear-resistant coatings are measured using the 3ω method in the temperature range 80<T<600 K. The coatings are 13 μm thick and deposited by chemical vapor deposition on substrates of Co-cemented WC. The α-Al2O3 coating has a thermal conductivity comparable to sapphire at T>300 K. The relatively smal...

The theoretical minimum thermal conductivity can be used to model heat transport in a wide variety of bulk and thin-film materials with strong atomic-scale disorder. To explore the possibility of using metastable microstructures in thin-film materials to achieve significant reductions in conductivity, we present experimental results - obtained usin...

The thermal conductivity of pulsed laser deposited SrTiO3 thin films is measured in the temperature range 30-400 K using the 3ω method. The room temperature thermal conductivity of the films are more than twice smaller than that of SrTiO3 bulk crystal. At low temperatures, the film thermal conductivity behaves much like amorphous bulks. We observe...

The thermal conductivity of Si–Ge superlattices with superlattice periods 30≪L≪300 Å, and a Si _0.85 Ge _0.15 thin film alloy is measured using the 3 ω method. The alloy film shows a conductivity comparable to bulk SiGe alloys while the superlattice samples have a thermal conductivity that is smaller than the alloy. For 30≪L...

Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3ω method. SiO2 and SiNx films are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films >100 nm thick, the thermal conductivity shows little dependence on film thickness: the thermal c...

To gain a better understanding of heat transport in optoelectronic and microelectronic devices, we have measured the thermal conductivity of chemical vapor deposited (CVD) SiO2 and SiNx thin films, 20-200 nm thick, using an extension of the 3omega method. For film thicknesses 100 nm thick show little thickness dependence. This behavior is attribute...

The thermal conductance of 8- to 200-nm-thick films of SiO and MgO is measured in the 2 temperature range 78 - 400 K using the 3 omega method. The apparent thermal conductivity of the films is reduced by the finite thermal conductance of the interfaces between the metal film heater and the dielectric layer, and between the dielectric layer and the...

The 3w method is used for the thermal conductivity measurement of ultra thin dielectric films of SiO2 and MgO. The films are deposited on a small opening of Si substrate covered with 200 nm thick insulation layer. This method greatly reduced the probability of getting short-circuited between the heater and Si substrate. With this improvement, the 3...

The thermal conductivity of oxide thin films deposited using dc, rf, and ion-beam sputtering is measured in the temperature range 80--400 K using the 3{omega} method. Thermal conductivity data for amorphous thin films of SiO{sub 2} are nearly identical to bulk {ital a}-SiO{sub 2}. Data for amorphous Al{sub 2}O{sub 3}, while having a magnitude and t...

The complex diclcctric constants of (NH4)2SO4 have been measured in the temperature range from 350 K to 450 K along a, b and c axes with a frequency range from 10 kHz to 4 MHz. The frequency dependent dielectric anomaly at about 417 K with an anomaly at 408 K was observed. The heat capacity and the thermal conductivity were also measured in this te...

We have developed the technique, called 3ω method, capable of measuring the dynamic specific heat of a solid in the frequency range from 0.01 Hz to 2 kHz and used this technique to measure the specific heat of KH2PO4 as a function of frequency. The specific heat becomes frequency-dependent near the Curie point.

A new ac calorimetry for dielectric solids was developed. A long and thin metal strip directly evaporated onto the surface of the sample is used as a heater and thermometer. Temperature oscillation of the heater is measured from the third harmonic voltage at the heater. Both the heat capacity and thermal conductivity of the sample are obtained by t...

A new digital circuit for fast and stable frequency tripling was constructed. The frequency tripler covers the input frequency range from 0.1 Hz up to 5 kHz with a maximum phase shift less than 1 deg at the highest frequency. The tripler generates a stable signal synchronized to the input after just one input period. Since the circuit design is fle...

The thermal conductivity of KH2PO4 (Potassium Dihydrogen Phosphate, KDP) single crystal under dc bias fields up to 2 kV/cm was measured using a novel technique called the 3ω method. Without a bias field, a small but definite discontinuity was observed at the Curie temperature (Tc = 123 K), indicating the first-order nature of the transition. The va...

We have utilized a new technique, called the 3omega method, to measure the thermal conductivity of insulating solids, triglycine sulfate (TGS) and sodium chloride (NaCl). The method uses, as a heater and sensor simultaneously, a long and thin metallic wire directly evaporated onto the surface of a sample. An ac electric current at angular frequency...

The phase transitions in ferroelectric thiourea [SC(NH2)2] have been investigated using specific heat and dielectric constant measurements. For the measurement of specific heat, a calorimeter was built for ac calorimetry using an electrical heating method. The temperature dependence of the specific heat obtained for thiourea is in good agreement wi...