Hiện nay mật độ bóng bán dẫn trên một chíp ngày một tăng nên ngoài kỹ thuật quang khắc còn nhiều kỹ thuật khác cho phép khắc lên trên lớp cảm quang những chi tiết với độ phân giải và mức độ tinh vi tốt hơn rất nhiều như kỹ thuật e-beam lithography (kỹ thuật khắc dùng chùm điện tử), hoặc tia X. | LOGIC AND SWITCH SIMULATION Digital integrated circuits are designed to operate with binary representations for data. The basic presumption is that only two logic states are important for each signal line. Thus knowledge of a precise voltage versus time characteristic for each node in the circuit is not necessary to design or analyze digital circuits. For many purposes this simplifies both the circuits and their analysis compared to analog circuits. Nevertheless computer simulation and verification of a circuit s functionality are necessary. Even though a digital circuit is designed based on logic gates the logic gates arc fabricated from the basic transistors and conductors allowed by the integrated circuit process. Therefore it is often the case that the electrical operation of a simple logic circuit must be characterized by using a circuit simulator such as SPICE. Though circuit simulation of digital circuits is frequently used such circuit simulation has several drawbacks. As described in the previous section the large number of logic gates in most digital integrated circuits precludes circuit simulation of the entire system because of the extended computer time required. Also standard circuit simulators provide more detail about circuit voltages than is required to analyze a logic circuit. In an effort to reduce computer simulation time and to provide appropriate data to characterize the operation of digital circuits logic simulators were developed. Logic simulators allow specification of the operation of a circuit block in terms of its behavior. For example a simple logic gate is described by its behavior such as AND OR or NOT. More complex digital blocks such as full adders and multiplexers are each described by their corresponding behavior rather than their circuit structure. The circuit inputs arc specified as binary values that change at discrete time intervals Logic simulator outputs are provided as binary values as well. Pure logic simulation docs not .
