Question

55. Velocity saturation leads the MOSFET to reach operation in saturation at a smaller voltage Vps 56. The saturation current in short channel MOSFET's increases due to velocity saturation 57. The MOSFET transconductance is exponentially dependent on the drain current 58. In velocity saturation regime short channel MOSFET's transconductance are independent of the input voltage 59. Sub-threshold conduction in short channel MOSFET's relates to tunneling through the ultrathin oxide 60. Sub-threshold current is linearly dependent on the gate voltage 61. The charge interaction in the channel results in a larger threshold voltage of the short channel MOSFET's compared to long channel devices. 62. A dynamic memory cell is made of a single capacitance and a single transistor 63. The READ operation in a static memory cell is destructive 64. The READ operation from the memory cell is usually much slower than the write operation
true or false

Answer 1

55) velocity saturation leads the MOSFET to reach operation in saturation at a smaller voltage Vds: True • Velocity saturation occurs in any general solid state device when charged carriers move in a solid under the force of an electric field, they acquire a velocity proportional to the magnitude of this electric field. Channel carrier mobility can also be reduced by a high lateral electric field in the channel. This mobility degradation due the lateral field Ex (drain voltage) has a more significant effect on the device current equations than does the normal field Ex (gate voltage). This is because an increase in the lateral field eventually causes velocity saturation of the carriers. For a given normal field, the velocity v of a carrier is proportional to Ey, at low lateral fields, and the proportionality constant is the surface mobility us. However, as Ey increases, the carrier velocity tends to saturate. Carriers in the short channel devices reach the velocity saturation at lower values of Vds than for the long channel devices. This effect is due to the channel length reduction that implies the higher electric fields for the equivalent drain to source: The electric field within the channel is due to the voltage applied to the drain terminal. Due to this electric field Horizontal mobility also reduces.

56) the saturation current in short channel increases due to velocity saturation: • • • true The velocity of carriers are supposed to vary linearly with the applied electric field as the mobility is considered to be a constant parameter. in a short channel, due to excessive collisions suffered by the carriers, their velocity saturates after a critical electric field. Since current is the rate of flow of electrons, it also attains a saturated value once the velocity saturates. • 57) mosfet transconductance is exponentially depends on the drain current: • • False drain current depends quadratically on the gate voltage, the transconductance which is the derivative: d/p/dVG, depends linearly on VG above threshold for Ve>Vto, the drain current is well approximated by the quadratic, whereas for VG<VTO (i.e., sub-threshold) the drain current depends approximately exponentially on V6. Thus the drain current is not strictly zero below threshold, merely exponentially small.

58) in velocity saturation regime short channel MOSFET transconductance are independent of the input voltage: false • Velocity Saturation results in saturation of the current IDS, occurs mostly in short- channel MOSFETS velocity of carriers are supposed to vary with Electric field. which is generated by input voltage. so transconductance are dependent of the input voltage