Charge Retention Characteristics Research Articles

Charge trapping in plasma-polymerized thin films

The surface potential of freshly plasma-polymerized films of hexamethyldisiloxane was measured for film thicknesses ranging from about 0.1 to 1 μm. The films are found to be in an electret state under certain fabrication conditions. Experimental evidence is given which indicates that charge trapped during plasma polymerization is uniformly distributed across the sample thickness. It has been found that other electret properties such as the polarity of trapped charge, and the charge retention characteristics can also be controlled by an appropriate choice of polymerization conditions.

Effects of High Temperature Hydrogen Annealing on n-Channel Si-Gate MNOS Devices

High temperature hydrogen annealing, rather than high temperature nitrogen annealing, is adopted as an essential technology for fabrication of n-channel silicon-gate MNOS memory devices offering excellent charge retention characteristics. Retention is greatly influenced by the annealing ambient and temperature after nitride deposition. In case of annealing in nitrogen or oxygen, higher temperatures cause a large amount of retention degradation, while in hydrogen, they do not degrade but improve retention. The high temperature hydrogen annealing decreases both Si–SiO2 interface state density and the Si3N4 conductivity. The interface state density greatly influences charge decay due to direct tunneling when the devices are tested at room temperature. The conductivity is influential at elevated temperatures. Long retentivity is evaluated and the results confirm a ten year nonvolatility at 125°C.

Static induction transistor image sensors

New image sensors, based on the operational principle of static induction transistor (SIT), are described in this paper. Two operational modes of SIT image sensors are described here. One is the electron-accumulation mode in which electrons are stored in the floating-cell region and another is the electron-depletion mode in which electrons are removed from the floating-cell region in response to optical input. The electron-depletion mode is superior to the electron-accumulation mode in the charge retention characteristics, its temperature dependence, and the operational tolerancy. The described SIT image sensors, which utilize the vertically configured SITM structure, are very promising for application in very-large-area image converters due to high-speed high-packing density, and wide dynamic range, and especially due to extremely low power dissipation.

Solid-state storage batteries

Investigations were conducted to study the feasibility of a solid-state battery system for storage applications. During the development of various high energy density solid-state batteries we noted that the solid electrolyte material, LiI dispersed in large surface area Al2O3, has a high ionic conductivity at elevated temperatures, (for example 0.1Ω−1 cm−1 at 300° C) and is suitable for high-rate storage battery applications. In solid-state battery systems both the electrodes and electrolytes are in the solid state under the operating conditions of the battery. The absence of any liquid phase makes the individual cell containers unnecessary in a multicell battery resulting in a simplified battery structure and increased package efficiency. Furthermore, no material compatibility problem is encountered in the system. As a result, the solid-state battery system has excellent charge retention characteristics and a long projected operating life. Solid-state test cells, Li-Si/LiI(Al2O3)/TaS2/Ta, Li-Si/LiI(Al2O3/TiS2/Ti and Li-Si/LiI(Al2O3)/TiS2, Sb2S3, Bi were constructed and subjected to discharge-charge cycle tests at 300±10° C, at 13·7 mA cm−2. Preliminary test results demonstrated that these solid-state battery systems are rechargeable and may be suitable for both load levelling and/or vehicle propulsion. From the considerations of material availability and cost and operational efficiencies it was concluded that the Li-Si/LiI(Al2O3)/TiS2, Sb2S3, Bi system is most suitable among the three systems studied for the development of practical storage batteries. Preliminary design studies showed that practical energy densities of 200W h kg−1 and 520 W h l−1 can be realized with the Li-Si/TiS2, Sb2S3, Bi storage batteries.

Charge transfer properties of mnos structures as influenced by processing parameters

The charge transfer and retention characteristics of MNOS structures have been studied as a function of specified processing parameters utilized when fabricating the tunneling silicon oxide and charge storage silicon nitride layers. A grid array of n+ junctions fabricated on 2 ohm-cm “p” type silicon substrates allowed simulation of the transient characteristics of FET’s. Electrical measurements included switching speed, static and dynamic charge storage windows, and stored charge retention with time. The switching speed and window width were influenced by some processing parameters. Some shortcomings with recent discharge models are noted, based upon the data obtained. Limited (multiple cycling) “fatigue” studies have indicated improved window behavior with increased write-erase voltages, and pulse widths below one microsecond, for MNOS structures with the tunneling oxide prepared within an NO plus H2 ambient.

Charge storage characteristics of MIS structures employing dual-insulator composites of HfO2–SiO2 and SrTiO3–SiO2

Two MIS versions have been fabricated employing rf-sputtered dual insulator structures comprised of 1000 Å HfO2-20 Å SiO2 and 1000 Å SrTiO3-20 Å SiO2. The high-dielectric-constant insulators in combination with a 20-Å layer of silicon dioxide permit the transfer of charge by tunneling into traps at the dual-insulator interface to occur at considerably lower voltages than comparable structures employing silicon nitride or aluminum oxide. It was found that trap density and, hence, the degree of flat-band voltage shift could be altered by sputtering 50-Å layers of selected materials at the insulator-SiO2 interface. The devices employing hafnium dioxide show promise in an application as a nonvolatile electrically alterable memory element. Although the strontium titanate devices exhibit a low threshold voltage for onset of charge transfer, the charge retention characteristics are poor.