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A method to investigate the nature and level of the turbulence in the core of hot tokamak plasmas is discussed. The method is based on the energy-resolved observation of superthermal electrons by means of vertical electron cyclotron emission. The sensitivity of the electron distribution function and of the related emission spectra to both electrostatic and magnetic turbulence is first investigated theoretically. Then, the method is applied to the study of electron cyclotron resonance heated plasmas in the TEXT-U tokamak. All the measured spectra appear to be dominated by effects due to magnetic rather than to electrostatic turbulence. The experimental spectra are compared with the results of 3D Fokker-Planck simulations including radial diffusion, and the corresponding levels of magnetic turbulence are deduced.

IntroductionAs CMOS technology is scaled to the 90nm node and beyond, silicon nanocrystal nonvolatile memories are receiving increased attention as a replacement for floating gate nonvolatile memories [1,2]. The thin dielectrics in these memories can lead to excessive gate disturb during the read operation. Of primary concern is the loss of electrons of the program state to the gate through the top oxide overlying the nanocrystals. This loss is the result of tunneling due to the high electric field between the gate and the nanocrystals. It has been shown that reducing the natural threshold voltage (V t,nat ) of the memory cell leads to a reduction in gate disturb [3]. Simple reduction of the V t,nat by decreasing the substrate doping concentration can result in severely degraded short channel performance, as well as degraded hot carrier injection (HCI) performance during the program operation. Thus, it is desired to construct a substrate doping profile with a light surface concentration to obtain a low V t,nat , and a heavy doping concentration just below the surface to provide robust short channel performance and good HCI programmability.

Absfracf -Silicon nanocrystals provide opportunity to solve the challenging problem of tunnel oxide scaling of conventional Flash memories by increasing immunity to charge loss via tunnel oxide defects. New aspects in silicon nanocrystal memory technology include Coulomb blockade or charge confinement effects, atomistic nucleation, and nanocrystal passivation to preserve them during subsequent processing and progranderase endurance characteristics. This paper discusses the above characteristics and culminates in presenting salient results from 4 Mb NOR memory arrays fabricated using 90nm CMOS technology. Excellent memory characteristics including tight Vt distributions are obtained using a tunnel oxide thickness of Snm and a 6V power supply.