BY :K . SHIVA KUMAR REDDYP . MANOJ
VACUUM TUBE COMPUTER
THE FIRST TRANSISTOR
TRANSISTORIZED COMPUTER…
THE FUTURE ELECTRONICS
SINGLE ELECTRON TRANSISTORS
Source Drain
SiO2 Insulator (Glass) Gate
holes
electrons
5 volts
electrons to be transmitted
MOSFET OperationStep 1: Apply Gate Voltage
Step 2: Excess electrons surface in channel, holes are
repelled.
Step 3: Channel becomes saturated with electrons.
Electrons in source are able to flow across channel to Drain.
P
N N
SINGLE ELECTRON TRANSISTOR
COULOMB BLOCKADE BARRIER
• No electron on quantum dot Electrostatic energy = 0
• Electron put on the quantum dot Charge stored EC = E2/2Cdot
• EC acts as potential barrier.• This potential barrier is called COULOMB BLOCKADE BARRIER.
CONDITION 1
1.Thermal energy < Coulomb blockade barrier KBT < E2/2Cdot
For safety 10KBT < E2/2Cdot
For spherical capacitor C α d(diameter of dot)
CONDITION 2
2. Uncertainty in energy < charging energy
E < e2/2Cdot 1From uncertainity principle E. T ~ h/2
E ~ h/2 T E ~ h/2RCdot 2
Put 2 in 1 h/2RCdot < e2/2Cdot R > h/e2
Hence R > 26kohm
OPERATION OF SINGLE ELECTRON TRANSISTOR
STAGE 1 STAGE 2 STAGE 3
STAGE 1:
STAGE 2:
Applying negative voltage
Applying positive voltage
FERMI LEVELS IN STAGE 2 :
STAGE 2:
Applying negative voltage
Applying positive voltage
Applying positive voltage
FERMI LEVEL IN STAGE 3:
Gate voltage and current relation
curre
nt
Gate voltagee2/2Cdot 2e2/2Cdo
t3e2/2Cdot
ADVANTAGES
• Power consumption
• Memory cells
• Size
• Heat dissipation
K . SHIVA KUMAR REDDYP . MANOJ