A simple Flash memory cell model for transient circuit simulation
A simple Flash memory cell model for circuit simulation is presented. The proposed model gives an excellent fitting of dc and transient data and does not require additional simulation time comparing with that of a MOSFET transistor. Effective control-gate voltage method and ideal current-mirror technique are introduced to calculate floating-gate voltage. These allow macro modeling of a Flash memory cell in a circuit simulator.
Flash memory device: Electrical modeling and simulation
Flash memory, created in the early eighties and based upon EEPROM, has become a very popular non-volatile memory since the start of the millennium. A Flash memory cell consists of 1 MOS transistor with a floating gate. The floating gate (in between the channel and the control gate) is able to trap electrons due to writing mechanisms (e.g. Fowler Nordheim and Channel Hot Electron Injection) and hereby changing the threshold level of the transistor. Flash also has different cell array architectures that define its read and write speed, and geometrical size. The array architectures called NOR and NAND are currently most popular. NOR is advantageous for high speed read and writing, however the NAND architecture is more compact and therefore more suitable for mass data storage. By creating a functional model of a Flash memory device, design of an electrical Flash memory device and its simulation can be simplified. After studying Flash cell models in literature, a Flash cell model and complete memory device will be presented in this Thesis. This study has also led to distinction between "Static" and "Dynamic" Flash cell models. Static models need a voltage or current source to change the threshold voltage. This results in 2 models, one for writing and another for reading. Dynamic models can use equations as behavioral blocks to ensure a threshold voltage change at the transistor and have one model to represent both reading and writing. In order to show simulation results of a Flash memory device, a 2x2 bit NOR and 1x2 bit NAND will be presented for analysis. Both with a dynamic cell model. Fowler Nordheim and Channel Hot Electron Injection are also taken into account in the presented net lists. The simulations have been done in HSPICE, an industrial version of SPICE (Simulation Program with Integrated Circuit Emphasis).
Thrombus formation after aortic valvular replacement using Björk-Shiley valve occluding the right coronary orifice.
We describe a patient with unstable angina due to occlusion of the orifice of the right coronary artery by thrombus formation after aortic valvular replacement using a Björk-Shiley valve. After strict anticoagulant treatment, transesophageal echocardiography demonstrated disappearance of the thrombus formation around the orifice of the right coronary artery.