Study on the Novel PRAM cell structure for reducing reset current

본 논문에서는 차세대 메모리인 상변화 메모리(Phase change random access memory)의 지우기 전류 감소를 위한 새로운 셀 구조에 관해 고찰하였다. 기록, 소거, 재생 속도, 재기록, 횟수 등을 포함한 성능에서 DRAM 급의 성능 특성을 가지며 소자구조 및 제작공정이 단순하여 정보저장 및 처리 용량대비 저가격화 달성이 용이한 상변화 메모리(PRAM)가 차세대 비휘발성 메모리로 주목 받고 있다. 그러나 상변화 메모리의 지우기 동작전류는 타 메모리 소자에 비해 큰 값을 나타내는 단점이 있어 상변화 메모리가 기존의 메모리 소자를 대체하기위한 경쟁력을 갖추기 위해서는 지우기 동작 전류를 낮추어야 한다. 상변화 메모리의 지우기 동작 전류를 낮추기 위해 상변화 물질, 발열전극 물질 및 셀 구조 변화 등의 연구가 진행 중이다. 그 중에서 셀 구조를 변형함으로써 지우기 전류를 줄여보고자 하는 연구가 이루어지고 있다. 본 연구는 PRAM의 지우기 전류를 줄이기 위해 상변화 물질 자체를 발열체로 사용하는 Pore형 PRAM 소자를 제작하여 소자 특성을 조사하였다. 또한 3차원 유한 요소 해석 프로그램을 이용하여 나노 스케일 PRAM의 GST박막의 두께에 따른 PRAM의 지우기 전류와 온도에 관해 조사하였고, 상변화 물질의 두께가 얇아질수록 지우기 전류가 증가하는 것을 알게 되었다. 지우기 전류의 증가를 막기 위해 SiO₂ 열 방지층을 사용하는 새로운 구조의 PRAM cell을 제안하였고 또한 지우기 전류와 온도에 관한 조사를 하였다. 200 ㎚ 의 두께의 GST박막의 두께에서 기존의 구조와 새로운 구조의 PRAM을 비교하였을 때, 새로운 구조의 PRAM cell에서 온도는 536.60 ℃ 에서 817 ℃ 로 크게 증가하였고, 지우기 전류는 17.4 ㎃ to 13.7 ㎃ 로 감소하였음을 알 수 있었다. 이 결과는 새로운 구조의 PRAM cell이 열 방지층으로서 효과적으로 작용해 지우기 전류를 감소시킴을 알 수 있었다.Today, the market for non-volatile memory is dominated by the Flash technology. Due to the increasing cost of down scaling Flash technology, the memory industry is searching for alternative memory concept. One of most promising candidates is the electrical phase change technology PRAM. In this paper, we fabricated the PRAM unit cell and investigated electro and thermal characteristics of PRAM unit cell with novel structure using SiO₂ heat blocking layer. As thickness of GST thin film decreased from 400 ㎚ to 300 ㎚, reset current and temperature changed a bit but did not affect so much memory cell operation. But as thickness of GST thin decreased from 300 ㎚ to 200 ㎚, reset current increased from 15 ㎃ to 17.4 ㎃ and temperature decreased from 704.86 ℃ to 536.60 ℃. As reset current and temperature changed like at 200 ㎚ thickness of GST thin film, the memory cell operation did not work as normal. From this results, we investigated material parameters of heater electrode for why reset current and temperature changed. After investigation, we found that heat which was generated between phase change material GST and heater electrode TiN was given to top electrode W due to thin thickness of GST thin film. We have throughly investigated the decreasing of temperature of 200 ㎚ thickness of GST thin film and found that the severe heat loss occurred at top electrode. In the case of 200 ㎚ thickness of GST thin film, a heat rapidly transferred to top electrode before melting temperature. A heat which contacted with top electrode transferred easily to outside and temperature decreased. Therefore, novel structure PRAM which deposited SiO₂ blocking layer instead of part of top electrode was proposed. The SiO₂ blocking layer which is dielectric layer can protect the heat to give off through top electrode. In comparison with conventional PRAM at 200 ㎚ GST thin film thickness, temperature of novel structure PRAM highly increased from 536.60 ℃ to 817 ℃ and reset current of novel structure PRAM decreased abruptly. from 17.4 ㎃ to 13.7 ㎃. This result shows that novel SiO₂ blocking layer of PRAM successfully protected heat to give off to top electrode.Chapter 1. Introduction = 1 Chapter 2. What is the PRAM = 4 2.1 Definition and background of the PRAM = 4 2.2 Theory of operation = 7 2.3 Method of reduction of reset current = 11 2.4 Electromagnetic analysis = 12 2.5 Thermal analysis = 14 Chapter 3. Experimental = 17 3.1 Fabrication procedure = 17 3.2 Finite element analysis = 21 Chapter 4. Results and discussion = 24 4.1 Electro-thermal characteristics of the PRAM = 24 4.1.1 Electrical property = 24 4.1.2 Electro-thermal analysis = 27 4.1.3 Effect of thickness of Ge2Sb2Te5 = 29 4.2 Effect of novel structure PRAM unit cell with heat blocking layer = 33 4.2.1 Finite element analysis model = 33 4.2.2 Electro-thermal analysis = 34 4.3 Effect of heat blocking layer in planar type PRAM = 38 4.3.1 Electro-thermal analysis = 38 4.3.2 Effect of heat blocking layer = 41 Chapter 5. Conclusion = 45 Chapter 6. Reference = 4

Inflammatory Responses in the Muscle Coat of Stomach and Small Bowel in the Postoperative Ileus Model of Guinea Pig

PURPOSE: Small intestinal function returns first after surgery, and then the function of the stomach returns to normal after postoperative ileus (POI). The aim of this study was to investigate inflammatory responses in the muscle coat of stomach and small intestine in guinea pig POI model. MATERIALS AND METHODS: The distance of charcoal migration from pylorus to the distal intestine was measured. Hematoxylin and eosin (H&E) and immunohistochemical stain for calprotectin were done from the histologic sections of stomach, jejunum and ileum obtained at 3 and 6 hour after operation. Data were compared between sham operation and POI groups. RESULTS: The distance of charcoal migration was significantly reduced in the 3 and 6 hour POI groups compared with sham operated groups (p<0.05). On H&E staining, the degree of inflammation was significantly higher in the stomach of 3 hour POI groups compared with jejunum and ileum of POI groups or sham operated groups (p<0.05). Calprotectin positive cells were significantly increased in the muscle coat of stomach of 3 hour POI groups compared with jejunum and ileum of POI groups or sham operated groups (p<0.05). There was strong association between the degree of inflammation and calprotectin positive cells in stomach. CONCLUSION: Postoperative ileus induced by cecal manipulation significantly increased the degree of inflammation and calprotectin positive cells in the muscle coat of stomach as a remote organ. The relevance of degree of inflammation and the recovery time of ileus should be pursued in the future research.ope

A Case of Pancreatic Metastasis From a Papillary Thyroid Carcinoma Mimicking Pancreatic Cancer

Papillary thyroid cancer (PTC) has a good prognosis and a low incidence of distant metastases. It is extremely rare for PTC to metastasize to the pancreas. Only five cases have been previously reported worldwide. Most cases are discovered incidentally by abdominal computed tomography (CT) or positron emission tomography-CT (PET-CT) during follow-up studies after thyroidectomies. Pancreatic metastasis of PTC is usually unidentifiable by a whole-body I131 scan, a common follow-up modality. When a pancreatic mass is found in patients with PTC, it must be differentiated from pancreatic cancer. In previous reports, patients with pancreatic metastases of PTC underwent operations for therapeutic diagnosis or underwent fine needle aspiration biopsies (FNAB). However, it is unclear whether the benefit of an operation outweighs the risk. We experienced a case of PTC with pancreatic metastasis that was found on PET-CT. Contrast-enhanced endoscopic ultrasonography (EUS) was performed to evaluate the characteristics of the pancreatic mass and pathological confirmation was obtained cytologically via EUS-FNA.ope

기니 픽의 수술 후 장폐색 모델에서 위장, 소장의 근육층 내 염증 변화

Dept. of Medicine/석사Purpose: Small intestinal function returns first after surgery, and then thefunction of the stomach returns to normal after postoperative ileus (POI). Theaim of this study was to investigate inflammatory responses in the muscle coatof stomach and small intestine in guinea pig POI model.Materials and Methods: The distance of charcoal migration from pylorus tothe distal intestine was measured. Hematoxylin and eosin (H&E) andimmunohistochemical stain for calprotectin were done from the histologicsections of stomach, jejunum and ileum obtained at 3 and 6 hour afteroperation. Data were compared between sham operation and POI groups.Results: The distance of charcoal migration was significantly reduced in the 3and 6 hour POI groups compared with sham operated groups (p<0.05). OnH&E staining, the degree of inflammation was significantly higher in thestomach of 3 hour POI groups compared with jejunum and ileum of POIgroups or sham operated groups (p<0.05). Calprotectin positive cells weresignificantly increased in the muscle coat of stomach of 3 hour POI groupscompared with jejunum and ileum of POI groups or sham operated groups(p<0.05). There was strong association between the degree of inflammation2and calprotectin positive cells in stomach.Conclusion: Postoperative ileus induced by cecal manipulation significantlyincreased the degree of inflammation and calprotectin positive cells in themuscle coat of stomach as a remote organ. The relevance of degree ofinflammation and the recovery time of ileus should be pursued in the futureresearch.ope

Trying to win the war against antibiotics resistance

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상아모세포의 조건배지를 이용한 백악모세포의 분화와 석회화 조절

For the regeneration of periodontal tissues, the microenvironment for new attachment of connective tissue fibers should be provided, At this point of view, cementum formation in root surface plays a key role for this new attachment. This study was performed to figure out which factor promotes differentiation of cementoblast Considering anatomical structure of tooth, we selected the cells which may affect the differentiation of cementoblast - Ameloblast, OD11&MDPC23 for odontoblasts, NIH3T3 for fibroblsts and MG63 for osteoblasts. And OCCM30 was selected for cementoblast cell line. Then, the cell lines were cultured respectively and transferred the conditioned media to OCCM30. To evaluate the result, Alizarin red S stain was proceeded for evaluation of mineralization. The subjected mRNA genes are bone sialoprotein(BSP), alkaline phosphate(ALP) , osteocalcin(OC), type I collagen(Col I), osteonectin(SPARC ; secreted protein acidic and rich in cysteine). Expression of the gene were analysed by RT-PCR, The results were as follows: 1. For alizarin red S staining, control OCCM30 didn't show any mineralized red nodules until 14 days. But red nodules started to appear from about 4 days in MDPC-OCCM30 & OD11-OCCM30. 2. For results of RT-PCR, ESP mRNAs of control-OCCM30 and others were expressed from 14 days, but in MDPC23-OCCM30 & OD11-OCCM30 from 4 days. Like this, the gene expression of MDPC23-OCCM30 & OD11-OCCM30 were detected much earlier than others. 3. For confirmation of odontoblast effect on cementoblast, conditioned media of osteoblasts(MG63) which is mineralized by producing matrix vesicles didn't affect on the mineralized nodule formation of cementoblasts(OCCM30). This suggest the possibility that cementoblast mineralization is regulated by specific factor in dentin matrix protein rather than matrix vesicles. Therefore, we proved that the dentin/odontoblast promotes differentiation/mineralization of cementoblasts. This new approach might hole promise as diverse possibilities for the regeneration of tissues after periodontal disease.본 연구는 교육인적자원부 누리사업 국고보조금으로 수행한 과제입니다