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11 và 12. Phân tích tương tự của các mạch đồng bộ từ quan điểm thời gian có thể được tìm thấy trong Refs. 45 đến 49. Ngăn chặn việc đến trễ của tín hiệu dữ liệu trong một đường dẫn dữ liệu địa phương với Flip-flops hoạt động của các Rf Ri đường dẫn dữ liệu địa phương thể hiện trong hình. 1,14 đòi hỏi rằng bất kỳ tín hiệu dữ liệu đang được lưu trữ trong Rf đến các dữ liệu đầu vào. | Flash Memories 5-19 Solving Eqs. 5.22 and 5.24 with the assumption that only electrons at the Fermi level contribute to the current yields the Fowler-Nordheim formula for the tunneling current density Jtunnei at high electric field tunnel q-E2 DB3 --- exp J - I 16 7t2 3 h q E 5.25 This equation can also be expressed as J tunnel a 2 exp Ị k EJ 5.26 where a and B are Fowler-Nordheim constants. The value of a is in the range of 4.7X10-5 to 6.32X10-7 A V2 and B is in the range of 2.2X108 to 3.2x108V cm.47 The barrier height and tunneling distance determine the tunneling efficiency. Generally the barrier height at the Si-SiO2 interface is about 3.1 eV which is material dependent. This parameter is determined by the electron affinity and work function of the gate material. On the other hand the tunneling distance depends on the oxide thickness and the voltage drop across the oxide. As indicated in Eq. 5.26 the tunneling current is exponentially proportional to the oxide field. Thus a small variation in the oxide thickness or voltage drop would lead to a significant tunneling current change. Figure 5.22 Shows the Fowler-Nordheim plot which can manifest the Fowler-Nordheim constants a and B. The Si-SiO2 barrier height can be determined based on this FN plot by quantum-mechanical QM modeling.48 5.4.3 Comparisons of Electron Injection Operations As mentioned in the above section there are several operation schemes that can be employed for electron injection whereas only FN tunneling can be employed for ejecting electrons out of the floating gate. Owing to the specific features of the electron injection mechanism the utilization of an electron injection scheme thereby determines the device structure design process technology and circuit design. The main features of CHEI and FN tunneling for n-channel Flash memory cell and also CHEI and BBHE injection for p-channel Flash memory cell are compared in Tables 5.1 and 5.2. 5.4.4 List of Operation Modes The employment of .