MICROELECTRONICS and NANOTECHNOLOGY (MN)

Question 3: Field Effect Devices

August 2009

## Questions

All questions are in this link

# Solutions of all questions

a) Previous year question.\\ b) $V_T = -1V$ So consider p-channel MOSFET.

$=\mu_pC_{ox}\frac{W}{L} = \mu_p\frac{\epsilon_{ox}}{t_{ox}}\frac{W}{L}$

\begin{align*} & t_{ox} \uparrow k\downarrow\\ & \mu_p \uparrow k\uparrow\\ & L \uparrow k\downarrow\\ & W \uparrow k\uparrow\\ & N_A \uparrow \text{ No change} \end{align*}

$V_{TH} = \psi_s+\frac{k_s}{k_{ox}}x_0\sqrt{\frac{2qN_A}{k_s\epsilon_0}\psi_s}$

chk only 2

f) square law $$Q_i=C_{ox}(V_{GS} - V_{th}-V)$$

n-channel

Bulk charge

$Q_i = -C_{ox}(V_{GS} - V_{th}-V))+\underbrace{qN_A[w_T(V)-w_T(V=0)]}_{\text{variation of$w_T$with$V$is considered}}$

------------------------------------------------------------------------------------


3)i)

Turned on without any applied gate voltage.

ii)

Better control on channel due to lowered body effect.

iii)

Very high speed device due to $e^-$ gas formation.

iv)

Can handle short channel effect much better

------------------------------------------------------------------------------------