Impact of relaxation on the performance of GeSe true random number generator based on Ovonic threshold switching

Volatile Ovonic threshold switching (OTS) are promising not only as the selector in crossbar resistive switching memory arrays, but also as true random number generators (TRNG) by utilizing its probabilistic switching characteristics. However, investigation on the reliability of OTS-based TRNG is still lacking, which hinders its practical application. Previously, we found that switching probability is dependent on the pulse amplitude and width. In this work, we report that relaxation which happens during the time interval between pulses can cause switching probability drift. Optimizing the bit-generation waveform and modulating the pulse conditions could provide a practical solution, in addition to the impact of external bias and temperature. This work provides useful guidance for the practical design and operation of OTS-based TRNGs

New Insights of the Switching Process in GeAsTe Ovonic Threshold Switching (OTS) Selectors

Experimental evidence and analysis in this work provide new insights into the fast switching process in GeAsTe ovonic threshold switching (OTS) selectors. For the first time, the full switching-OFF process, covering the defect cluster shrinking and rupture stages, can be measured and characterized. Two distinct switch-OFF mechanisms and their dependence on the total impedance of the selector and resistor (1S1Rs) circuit are identified. The impact of series resistance value on the switching process, the 1S1Rs operation, and the underlying mechanisms can be explained by the dynamic resistance of OTS that is induced by the transition of defect clusters. This research sheds new light on OTS switching mechanism and its impact on 1S1Rs operation

Acromegaly

Acromegaly is an acquired disorder related to excessive production of growth hormone (GH) and characterized by progressive somatic disfigurement (mainly involving the face and extremities) and systemic manifestations. The prevalence is estimated at 1:140,000–250,000. It is most often diagnosed in middle-aged adults (average age 40 years, men and women equally affected). Due to insidious onset and slow progression, acromegaly is often diagnosed four to more than ten years after its onset. The main clinical features are broadened extremities (hands and feet), widened thickened and stubby fingers, and thickened soft tissue. The facial aspect is characteristic and includes a widened and thickened nose, prominent cheekbones, forehead bulges, thick lips and marked facial lines. The forehead and overlying skin is thickened, sometimes leading to frontal bossing. There is a tendency towards mandibular overgrowth with prognathism, maxillary widening, tooth separation and jaw malocclusion. The disease also has rheumatologic, cardiovascular, respiratory and metabolic consequences which determine its prognosis. In the majority of cases, acromegaly is related to a pituitary adenoma, either purely GH-secreting (60%) or mixed. In very rare cases, acromegaly is due to ectopic secretion of growth-hormone-releasing hormone (GHRH) responsible for pituitary hyperplasia. The clinical diagnosis is confirmed biochemically by an increased serum GH concentration following an oral glucose tolerance test (OGTT) and by detection of increased levels of insulin-like growth factor-I (IGF-I). Assessment of tumor volume and extension is based on imaging studies. Echocardiography and sleep apnea testing are used to determine the clinical impact of acromegaly. Treatment is aimed at correcting (or preventing) tumor compression by excising the disease-causing lesion, and at reducing GH and IGF-I levels to normal values. Transsphenoidal surgery is often the first-line treatment. When surgery fails to correct GH/IGF-I hypersecretion, medical treatment with somatostatin analogs and/or radiotherapy can be used. The GH antagonist (pegvisomant) is used in patients that are resistant to somatostatin analogs. Adequate hormonal disease control is achieved in most cases, allowing a life expectancy similar to that of the general population. However, even if patients are cured or well-controlled, sequelae (joint pain, deformities and altered quality of life) often remain

Non-selective thin SiGe strain-relaxed buffer layers:Growth and carbon-induced relaxation

As an economically more attractive alternative to the classical thick graded strain-relaxed SiGe Buffer layers (SRB), we have developed a thin SRB based on a 200-nm-thick homogeneous Si0.8Ge0.2 layer with a C-doping spike inserted in about the middle of the layer. This C-doping layer enhances strongly the relaxation of the layer to similar to 80%, when compared to samples without C layer. The thin SRB shows threading defect densities <= 10(7)/cm(2) and a very smooth surface (RMS < 1 nm). The relaxation mechanism appears to be very similar to the "Modified Frank Read" (MFR) mechanism as developed by Legoues et al. [F. Legoues, B. Meyerson, J. Morar and P. Kirchner; J. Appl. Phys. 71 (1992) 4230.]. In our case, the MFR source for dislocation nucleation may consist of tiny SiC precipitates. (c) 2005 Elsevier B.V. All rights reserved