Digital CMOS Abbreviation E Alphabet Dictionary
EEPROM (Electrically Erasable Programmable ROM)
EEPROM is a non-volatile memory technology where data is stored using floating gate tunneling oxide transistors (FLOTOX). Programming in EEPROM is achieved through hot carrier injection, and erasure is performed by applying a high reverse voltage to the drain, causing Fowler-Nordheim tunneling into the substrate. EEPROMs have good write cycles but typically lower density due to the use of two transistors per cell (one for storage and one for access).
Effective Density of States
The effective density of states is a single numerical value representing how high the density of states would need to be at the edge of a semiconductor band to produce a charge concentration equal to that within the entire band.
Einstein’s Relationship
Einstein’s relationship recognizes the relationship between diffusivity and mobility in semiconductor physics. It acknowledges that both diffusivity and mobility are primarily functions of dopant concentration and that they are closely related.
Electrical Effort
An electrical effort is a unitless number used to quantify how much harder it is for a logic gate to drive itself when unloaded compared to driving an inverter. It is typically greater than or equal to 1, with only inverters having an electrical effort of 1.
Electromigration
Electromigration is a long-term degradation process in which high current density causes the corrosion of metal wires over time, leading to increased resistance or overheating. Electromigration is particularly problematic in semiconductor devices, especially in vias where improper etching can lead to narrower openings and higher resistance.
Electron
In general, an electron is a negatively charged subatomic particle found outside the nucleus of an atom. In the context of electrical current flow, an electron typically refers to a free electron functioning as a charge carrier in a semiconductor. In solid-state physics, these electrons can exist in the conduction band, allowing them to move in response to an electric field.
Electron Affinity
Electron affinity is the energy difference between the vacuum level and the edge of the conduction band in a semiconductor material. It represents the energy required to release the least energetic free electron from the material. Electron affinity is specific to the crystal material and remains independent of doping.
Electron Current
Electron current refers to the current resulting from the motion of electrons in the conduction band of a semiconductor material. This current can be due to either electron diffusion or electron drift, depending on the conditions.
Elmore Time-Constant
The Elmore time constant is a method used to calculate an equivalent time constant in a circuit with multiple capacitors and resistors. It is computed by multiplying each capacitance by the resistance seen in the intersection with the path to the output node. This method is useful for modeling delay in CMOS gates with significant internal node capacitance and in modeling delay in interconnects with substantial resistance.
Emitter
In a bipolar junction transistor (BJT), the emitter is one of the peripheral zones of the transistor. It is more heavily doped compared to the other regions (base and collector). In an NPN BJT, the emitter is n-type, while in a PNP BJT, it is p-type. The heavily doped emitter facilitates the injection of significantly more carriers into the base region than vice versa.
Emitter Efficiency
Emitter efficiency is the ratio of majority carriers to total carriers in the emitter current of a BJT. When the emitter doping is sufficiently heavy, this ratio approaches 1, indicating high efficiency in carrier injection.
Empty Flag (FIFO)
In a First-In-First-Out (FIFO) memory structure, the empty flag is a signal that indicates when the FIFO is empty. It tells the receiver that there is no unread data left in the memory. The FIFO is considered empty when an update to the read pointer causes it to become equal to the write pointer. Calculating the empty flag typically involves synchronizing pointers from different clock domains.
Enhancement Load Logic
Enhancement load logic is a type of ratioed logic family where the driver is an NMOS transistor and the load is a diode-connected NMOS transistor. While this logic family consists entirely of normal NMOS transistors, it exhibits poor steady-state performance. Logic low outputs are ratioed, and logic high outputs lose a threshold voltage drop from the supply, resulting in high static power dissipation.
Entity (VHDL)
In VHDL (VHSIC Hardware Description Language), an entity is the smallest building block that declares the existence of a specific circuit with defined ports. It does not provide information about the internal construction of the circuit or the number of instances used. Think of it as a description of the black box associated with the circuit.
Enumeration (VHDL)
In VHDL, enumeration is a user-defined data type that allows a signal to take on values from a finite set of textual labels defined by the user. These labels do not necessarily correspond to the hardware realization and are often left to the synthesizer’s optimization. Enumerations are commonly used in state machines to facilitate manipulation using state names rather than binary strings.
EPROM (Erasable Programmable ROM)
EPROM is a type of non-volatile memory with historical significance. EPROM devices typically use double-gate transistors with a relatively thick oxide layer. Programming was achieved through avalanche injection, while erasure required exposure to UV radiation. EPROMs had good programming speed and density but had limitations in write cycles and erasure times.
Erasure (NVMs)
Erasure in non-volatile memories (NVMs) refers to the process of resetting the state of a memory cell to its default state. This is typically achieved by removing charges from a floating gate (used in some NVM technologies) through methods such as UV exposure or Fowler-Nordheim tunneling.
ESD Protection (Electrostatic Discharge Protection)
ESD protection is a crucial component of input pin pad interface circuitry in electronic devices. It safeguards input pins from accumulating excessive static discharge, which can damage sensitive components. ESD protection is typically provided using two diodes that are reverse-biased under normal conditions but can break down reversibly to allow excess charge to dissipate safely.
Dry Etching
Dry etching is a process that uses plasmas to selectively remove material from a surface, typically metals like aluminum. It is highly directional, which allows for precise and dense pattern creation. Dry etching leaves no residue but can generate static charges, necessitating careful antenna design. Not all materials can be dry-etched effectively.
Wet Etching
Wet etching involves using wet solvents, often acids, to selectively remove material in a pattern. It is commonly used for silicon dioxide or silicon. Wet etching tends to be non-directional and can result in lateral etching, sometimes requiring post-etch cleaning.
Euler Path
In stick diagrams used in circuit design, an Euler path is a path that visits every transistor in both the Pull-Up Network (PUN) and Pull-Down Network (PDN) while visiting each node at most twice. Finding an Euler path simplifies the layout by allowing the use of a single diffusion strip per network. Multiple paths may require additional strips.
Evaluate Phase
In dynamic CMOS gates, the evaluate phase refers to the clock phase where the output node assesses the logic condition. During this phase, the output node’s capacitance either retains its precharge (if required by logic) or enters a high-impedance state.
Event (VHDL)
In VHDL (VHSIC Hardware Description Language), an event represents an actual change in the value of a signal. In a process, this change won’t occur until the end of the process (if a sensitivity list is used) or until the next wait statement is encountered otherwise.
Exit (VHDL)
In VHDL, “exit” is a loop manipulation construct that forces the loop to terminate immediately, regardless of the loop condition. It’s important to note that using “exit” can lead to unpredictable hardware synthesis results.
Exposure
Exposure refers to the process of illuminating a semiconductor wafer’s surface with light through a photomask. Typically, this light is of very short wavelength ultraviolet. The process must occur in a clean environment to prevent contamination of the photoresist.
