Gwan-Kyu Park

We present the successful fabrication of capacitive micromachined ultrasonic transducers (CMUTs) with an improved insulation layer structure. The goal is to improve device reliability (electrical breakdown) and device performance (reduced parasitic capacitance). The fabrication is based on consecutive thermal oxidation steps, on local oxidation of silicon (LOCOS), and on direct wafer bonding. No chemical-mechanical polishing step is required during the device fabrication. Aside from the advantag

This paper presents a comprehensive comparison between a collapse-mode and a conventional-mode capacitive micromachined ultrasonic transducer (CMUT); both devices have a 1-μm-thick silicon plate and operate at 10 MHz when biased at 100 V. The radii of the circular plates and the gap heights are modified to meet the design specifications required for a fair comparison. Finite element analysis (FEA) shows that the collapse-mode CMUT has higher output pressure sensitivity (46.5 kPa/V) than the conv

Interest in underwater transducers has persisted since the mid-1900s. Underwater transducers are designed in various shapes using various materials depending on the purpose of use, such as to achieve high power, improve broadband, and enhance beam steering. Therefore, in this study, an analysis is conducted according to the structural shape of the transducer, exterior material, and active material. By classifying transducers by structure, the transducer design trends and possible design issues c

This paper presents optimum design of circular membrane for high quality factor. A quality factor of CMUT, we designed for resonant chemical sensor, is dominated by Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">air</inf> and Q <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">support</inf> . We investigated these two factors independently. We calculate Q <inf xmlns:mml="http://www.w3.org/1998/Math/Mat

Accurate measurement of bladder volume is an important tool for evaluating bladder function. In this study, we propose a wearable bladder scanner system that can continuously measure bladder volume in daily life for urinary patients who need urodynamic studies. The system consisted of a 2-D array, which included integrated forward-looking piezoelectric transducers with thin substrates. This study aims to estimate the volume of the bladder using a small number of piezoelectric transducers. A leas

We present an improved fabrication method for capacitive micromachined ultrasonic transducers (CMUTs). Recently, a process was developed to fabricate CMUTs using direct wafer-bonding instead of the traditional sacrificial release method. This paper presents a method based on local oxidation of silicon (LOCOS) and direct wafer-bonding to improve the controllability of gap heights and the parasitic capacitance. Critical vertical dimensions are determined by a thermal oxidation process, which allow

Sepsis-associated acute kidney injury (AKI) is a leading cause of death in hospitalized patients worldwide. Despite decades of effort, there is no effective treatment for preventing the serious medical condition. Bee venom has long been used to treat a variety of inflammatory diseases. However, whether bee venom has protective effects against lipopolysaccharide (LPS)-induced AKI has not been explored. The aim of this study was to evaluate the effects of bee venom on LPS-induced AKI. The administ

Renal fibrosis is the principal pathological process underlying the progression of chronic kidney disease that leads to end-stage renal disease. Melittin is a major component of bee venom, and it has anti-bacterial, anti-viral, and anti-inflammatory properties in various cell types. Thus, this study examined the therapeutic effects of melittin on the progression of renal fibrosis using the unilateral ureteral obstruction (UUO) model. In addition, the effects of melittin on inflammation and fibro

Hyperlipidemia is a chronic disorder that plays an important role in the development of cardiovascular diseases, type II diabetes, atherosclerosis, hypertension, and non-alcoholic fatty liver disease. Hyperlipidemias have created a worldwide health crisis and impose a substantial burden not only on personal health but also on societies and economies. Transcription factors in the sterol regulatory element binding protein (SREBP) family are key regulators of the lipogenic genes in the liver. SREBP

We report on a capacitive resonant sensor with an oxide-nitride (ON) layer used as charge trap. The main idea is that we intentionally inject charges into the ON layer by biasing the device for 30 s with 160% of the pull-in voltage. We use a capacitive micromachined ultrasonic transducer (CMUT) to demonstrate this idea. The CMUT is fabricated via high temperature assisted direct wafer bonding after a local oxidation of silicon (LOCOS) to form evacuated cavities (vacuum gaps), and, thus, the devi

Acne vulgaris is the most common disease of the pilosebaceous unit. The pathogenesis of this disease is complex, involving increased sebum production and perifollicular inflammation. Understanding the factors that regulate sebum production is important in identifying novel therapeutic targets for the treatment of acne. Bee Venom (BV) and melittin have multiple effects including antibacterial, antiviral, and anti-inflammatory activities in various cell types. However, the anti-lipogenic mechanism

Cholangiopathy is a chronic immune-mediated disease of the liver, which is characterized by cholangitis, ductular reaction and biliary-type hepatic fibrosis. There is no proven medical therapy that changes the course of the disease. In previous studies, melittin was known for attenuation of hepatic injury, inflammation and hepatic fibrosis. This study investigated whether melittin provides inhibition on cholangitis and biliary fibrosis in vivo. Feeding 3,5-diethoxycarbonyl-1,4-dihydrocollidine (