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Published in Philip A. Laplante, Comprehensive Dictionary of Electrical Engineering, 2018
metal 2 the second layer applied in a fabrication process. In general the nth layer of the fabrication process is called metal n. metal halide molecule formed by the reaction of metals and halogen atoms. metal-electrode semiconductor field-effect transistor (MESFET) a specific type of FET that is the dominant active (amplifying) device in GaAs MMICs. An FET is composed of three terminals called the gate, drain, and source, and a conducting "channel." In an amplifier application, the source is connected to ground, and DC bias is applied between the drain and source causing a current to flow in the channel. The current flow is controlled and "modulated" by the AC or DC voltage applied to the gate. metal-insulator-metal (MIM) capacitor a capacitor, which has a thin insulator layer between two metal electrodes. Generally, this capacitor is fabricated in semiconductor process, and this insulator layer provides high capacitance. Two extreme behaviors of a capacitor are that it will act as an open circuit to low frequencies or DC (zero frequency), and as a short frequency at a sufficiently high frequency (how high is determined by the capacitor value). Also called a thin film capacitor. metal-organic chemical vapor deposition (MOCVD or OMCVD) a material growth technique that uses metal organic molecules in an atmospheric or low pressure growth chamber and a controlled chemical reaction on a heated substrate to grow a variety of II-VI, III-V, and group IV materials with atomic layer control. Used to create material structures for a variety of electronic and
Dynamic Random Access Memory (DRAM)
Published in Shimeng Yu, Semiconductor Memory Devices and Circuits, 2022
The evolution of the capacitor dielectric materials used in DRAM to understand the EOT scaling is discussed in the next. In retrospect, the silicon/insulator/silicon (SIS) structure was employed in the trench capacitor era, where the two electrodes were both heavily doped poly polysilicon and oxide/nitride/oxide (ONO) layered dielectric was used. Later toward the end of the trench capacitor era in the early 2000s, the metal/insulator/metal (MIM) structure was adopted. Starting from the stacked capacitor era, conductive TiN was used as a metal electrode and high-k dielectric materials such as Al2O3 were employed, which recently was switched to ZrO2 (or its alloys with HfO2). The dielectric constant of these optimized materials ranges from 20 to 30. As shown in Figure 3.18, EOT has been decreased from 2.8 nm to sub-0.6 nm (the Armstrong regime) thanks to the high-k dielectric material. Given the EOT = 0.6 nm, the high-k dielectric could relax the physical thickness to 3–5 nm; thus, the direct quantum tunneling current through the dielectric layer is much suppressed. It should be noted that a good SN capacitor should not only provide high capacitance, but also need to suppress leakage current for maintaining DRAM’s retention. Using even higher-k material such as TiO2 or SrTiO3 is undesired as there is a well-known trade-off between the permittivity and the bandgap of the dielectrics. Higher permittivity means narrower bandgap, and thus exponentially larger leakage current. Figure 3.19 shows the recent trends of EOT and AR for DRAM capacitor’s material and structure.
Recent progress in diamond radiation detectors
Published in Functional Diamond, 2022
In this section, we will introduce the characteristics of diamond radiation detectors and the parameters which determine their performance. Diamond radiation detectors have a structure consisting of high-purity diamond sandwiched between two electrodes. This structure is called MSM (Metal-Semiconductor-Metal) or MIM (Metal-Insulator-Metal) structure. In the field of radiation measurements, it is also called a solid-state ionization chamber because it operates on the same principle as gas ionization chambers. Figure 1 shows the schematic of the detector. When a charged particle is injected into the detector, it generates electron-hole pairs. The generated charge carriers move along the electric field. This movement of electrons/holes induces current following Shockley-Ramo theorem [15]. By detecting this induced current/charge, incidence of radiation can be obtained. The timing of the arrival of the radiation can be determined by the current pulse, and the energy of the radiation can be determined from the amount of charge. Since the amount of charge is linear to that of incident energy in the detector and energy spectrum is unique to nuclide, energy spectroscopy is a powerful tool to identify nuclide. The following is a list of performance specifications for diamond radiation detectors.