A nanoelectromechanical device incorporating the nanocrystalline silicon ͑nc-Si͒ dots is proposed for use as a high-speed and nonvolatile memory. The nc-Si dots are embedded as charge storage in a mechanically bistable floating gate. Position of the floating gate can therefore be switched between two stable states by applying gate bias. Superior on-off characteristics are demonstrated by using an equivalent circuit model which takes account of the variable capacitance due to the mechanical displacement of the floating gate. Mechanical property analysis conducted by using the finite element method shows that introduction of nc-Si dot array into the movable floating gate results in reduction of switching power. High switching frequency over 1 GHz is achieved by decreasing the length of the floating gate to the submicron regime. We also report on experimental observation of the mechanical bistability of the SiO 2 beam fabricated by using the conventional silicon etching processes.
Unified transient and frequency domain noise simulation of random telegraph noise and flicker noise is conducted using a multiphonon-assisted model that considers tunneling probabilities and energy transitions of discretized traps in the gate insulator of MOSFETs. The proposed model is able to concurrently represent the dynamic behavior of electron and hole trapping and detrapping via interactions with both the Si substrate and Poly-Si gate. The model is implemented in a 3-D device simulator to examine the effect of device structure and bias conditions. The conventional analytical model does not precisely estimate the noise powers in short-channel MOSFETs due to the nonuniform trapped charge effect. The high trap density near the shallow trap isolation edges is predicted quantitatively by comparing the measured data with the simulated data. In conclusion, we confirm the validity of the developed unified simulator and its usefulness for gaining insights into trap sites and noise reduction engineering.Index Terms-Device simulations, flicker noise, random telegraph noise (RTN), trap distribution.
, where L, T , and Z 0 represent the length, thickness, and equilibrium displacement of the buckled floating gate, respectively. We demonstrate that the switching frequency can be increased while maintaining the switching force when we downscale all the floating gate dimensions proportionally along with the scaling law. We also show that the switching voltage can be reduced down to less than 15 V while maintaining the ON/OFF operation range of the sense MOSFET by optimizing the cavity structure which sustains the inside buckled floating gate.
Technology ---Nano Electro-Mechanical Systems (NEMS) have a possibility of high-speed operation in the GHz regime since the characteristic frequencies are expected to increase with decreasing their dimensions [1]. We propose a new non-volatile memory concept based on bistable operation of the NEMS structure combined with nanocrystalline-Si (nc-Si) dots. Our new memory features a mechanically bistable floating gate beam, which incorporates the nc-Si dots as single-electron charge storage. The beam is suspended in the cavity under the gate electrode and moves via electrostatic interactions between the gate electrode and the charge in the nc-Si dots. Positional displacement of the beam is sensed via a change in the drain current of the MOSFET underneath. The switching speed between two stable states was estimated to be ~ 0.5 ns for a SiO 2 beam with the dimension of 1.0 × 1.0 × 0.1 μm 3 , from a mechanical analysis assuming the maximum central displacement of 35 nm. By optimizing both the beam structure and stored charge amount, we may build an extremely fast and non-volatile memory. A free-standing SiO 2 beam was successfully fabricated using a Si undercut etching technique. Most fabricated samples showed convex-shaped beams as a result of release of mechanical stress stored in SiO 2 after removing a Si layer underneath.Mechanical properties of the beam were investigated using a 3D finite element simulation [2]. We compared a nc-Si beam where a 2D nc-Si dot array was embedded inside a SiO 2 film and a simple poly-Si beam where a thin poly-Si sheet was placed between two SiO 2 layers. The maximum displacement obtained for the nc-Si beam under a constant uniaxial pressure was found larger than that for the poly-Si beam. This indicates that a larger displacement is achievable with the nc-Si beam when an electric field is applied via the gate bias and, therefore, the nc-Si beam has an advantage for low power operation.
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