Assumed that there is an A(l)/(S)i(O_(2))/(p)-Si metal-oxide-semiconductor (MOS) capacitor. Denote the permittivity
of SiO_(2)(Si) as epsi _(ox)(epsi _(Si)) and it is given that the thickness of SiO_(2) is t_(ox), the p-Si is uniformly doped to N_(A), and
the MOS capacitor can be regarded as one-dimensional.
(a) Given that the work function of the Al is slightly larger than chi _(Si), the electron affinity of Si, and assumed that the
oxide is perfect (completely insulating, no fixed charge/interface states within the oxide and at the interface),
please plot the band diagrams of the MOS capacitor when the MOS capacitor is biased at equilibrium and
threshold, respectively. You have to include E_(vac) (vacuum level), E_(c) (conduction band edge), E_(i) (intrinsic level),
E_(v) (valence band edge) and E_(F) (Fermi level) in you plots. Please also indicate on you plot the condition that the
MOS structure reaches threshold. (10%)
(b) Denote the work function of Al as Phi _(M). If there is now fixed charges density (per unit area) (Q_(F)) at the Si(O_(2))/(S)i
interface, write down, without derivation, the threshold voltage (V_(th)) for the MOS capacitor. Note that you have to
express the work function of Si in term of chi _(Si) and N_(A).(6%)
(c) Repeat (b), i.e., write down V_(th), for an A(l)/(S)i(O_(2))/(n)-Si structure, albeit with N_(A) replaced by N_(D). Denote again
the metal work function as Phi _(M) and express the work function of Si in term of chi _(Si) and N_(D)*(6%)
(d) Explain the difference between enhancement type and depletion type, for both n-channel MOSFET and p-channel
MOSFET, in term of threshold voltage. If the A(l)/(S)i(O_(2))/(p)-Si MOS structure in (a) is part of an MOSFET, is
this MOSFET enhancement type or depletion type? Repeat for the A(l)/(S)i(O_(2))/(n)-Si MOS structure in (c). ,
2%,2%
(e) Please explain what CMOS logics are and their advantages over p-MOS/n-MOS technology for VLSIs of high
integration level. (6%)
5.
Assumed that there is an Al / SiO, / p -- Si metal-oxide-semiconductor (MOS) capacitor. Denote the permittivity of SiO (Si) as &o.(&s: ) and it is given that the thickness of SiO, is tox, the p-Si is uniformly doped to N, and the MOS capacitor can be regarded as one-dimensional. (a) Given that the work function of the Al is slightly larger than Xst, the electron affinity of Si, and assumed that the oxide is perfect (completely insulating, no fixed charge/interface states within the oxide and at the interface), please plot the band diagrams of the MOS capacitor when the MOS capacitor is biased at equilibrium and threshold, respectively. You have to include Evac (vacuum level), Ec (conduction band edge), E; (intrinsic level) , E, (valence band edge)and EF (Fermi level) in you plots. Please also indicate on you plot the condition that the MOS structure reaches threshold. (10%) (b) Denote the work function of Al as . If there is now fixed charges density (per unit area) (QF) at the SiO/Si interface, write down, without derivation, the threshold voltage (V) for the MOS capacitor. Note that you have to express the work function of Si in term of Xs; and N4 . (6%) (c)Repeat (b), i.e., write down Vh , for an Al / SiO, /n -- Si structure, albeit with N replaced by Np . Denote again the metal work function as M and express the work function of Si in term of Xs: and Np : (6%) (d)Explain the difference between enhancement type and depletion type, for both n-channel MOSFET and p-channel MOSFET, in term of threshold voltage. If the Al / SiO, / p -- Si MOS structure in (a) is part of an MOSFET, is this MOSFET enhancement type or depletion type? Repeat for the Al / SiO, / n -- Si MOS structure in (c). (3%, 2%, 2%) (e).Please explain what CMOS logics are and their advantages over p-MOS/n-MOS technology for VLSIs of high integration level. (6%)
