Velocity Saturation Effects Velocity Saturation Effects Ohms Law
- Slides: 16
Velocity Saturation Effects
Velocity Saturation Effects Ohm’s “Law” • This says the Drift Velocity Vd is linear in the electric field E: μ Mobility • If this were true for all E, the charge carriers could be made to go fast without limit, just by increasing E! That would be nonsense! So, in every material, at high enough E, the Vd vs E curve must saturate to a constant value!
Ohm’s “Law” • Obviously, this says that the Vd vs E curve looks qualitatively like: E
• Measurement shows that, in all materials, at high enough E, the Vd vs E curve looks qualitatively like: Electrons Holes E
E Field Dependence of Drift the Velocity Saturation In n-type Si, the saturation velocity Vs ~ 107 cm/s at a field Es ~ 104 V/cm In Ga. As there is a velocity reduction (peak) before saturation. We’ll discuss this later The carrier velocity saturation at high E fields clearly places a FUNDAMENTAL upper limit on the speed of semiconductor devices.
A Simple Empirical Model for Velocity Saturation Or Vd μ(E)E Where μ(E) “Field Dependent Mobility” E << Esat, Vd = μE E << Esat, Vd constant
A Slightly Better Model for Velocity Saturation E << Esat, Vd = μE E << Esat, Vd constant
Still Another Model for Velocity Saturation: The Two Region Model
Velocity Saturation in Si • Measurements show that, at E 104 V/cm, the carrier velocity for electrons saturates to vsat 107 cm/s & for holes, it saturates to vsat 8 106 cm/s.
Velocity Saturation in Si • Measurements show that, at E 104 V/cm, the carrier velocity for electrons saturates to vsat 107 cm/s & for holes, it saturates to vsat 8 106 cm/s. To model the data, use
Velocity Saturation in Si • Measurements show that, at E 104 V/cm, the carrier velocity for electrons saturates to vsat 107 cm/s & for holes, it saturates to vsat 8 106 cm/s. To model the data, use Results
Temperature Dependence of Velocity Saturation in Si • Measurements: Both vsat & E are temperature dependent! Electrons
Temperature Dependence of Velocity Saturation in Si Holes
Voltage-Current Behavior in Velocity Saturation Conditions For short channel devices • As expected, in the linear, Ohm’s Law Region: I = V/R • In the non-linear Velocity Saturation Region, the I vs V curve bends over & saturates: I = Vsat/R = Isat
Qualitative I-V Curves in Velocity Saturation Conditions Long Channel Devices I Short Channel Devices I = V/R Vssat Vlsat V
I-V Curves in Velocity Saturation Conditions
- Ohm's law states
- Point form of ohms law
- Types of circuits and ohm's law
- Ohms law resistance
- Ohms law states that
- Defines ohm's law
- Watt
- Ohms law emf
- Electric circuit definition
- Ohms law introduction
- Ohms law worksheet
- A certain light bulb
- Derivation of ohm's law
- Triangulo de ohm
- Ohm's law quiz
- What is velocity saturation
- Vdssat