ece 875: electronic devices
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ECE 875: Electronic Devices. Prof. Virginia Ayres Electrical & Computer Engineering Michigan State University [email protected]. Lecture 27, 19 Mar 14. Chp 04: metal-insulator-semiconductor junction: GATES Examples. VM Ayres, ECE875, S14. VM Ayres, ECE875, S14. Chp. 04: MOS: Gate. - PowerPoint PPT PresentationTRANSCRIPT
ECE 875:Electronic Devices
Prof. Virginia AyresElectrical & Computer EngineeringMichigan State [email protected]
VM Ayres, ECE875, S14
Lecture 27, 19 Mar 14
Chp 04: metal-insulator-semiconductor junction: GATES
Examples
VM Ayres, ECE875, S14
Chp. 01: Si
Chp. 02: pn
Chp. 03: Interconnect
Chp. 04: MOS: Gate
VM Ayres, ECE875, S14
p-type Si
VM Ayres, ECE875, S14
Use energy band diagram to find:
p-type Si
VM Ayres, ECE875, S14
Use energy band diagram to find:
Electron concentration in channel
V requirements: battery = $
E –field/Vi across the insulator: breakdown not good
Q(x)
E (x)
V (x)
Everything else
Usual approach:
VM Ayres, ECE875, S14
= d E dx
∞ means deep in substrate
The total charge density is
The Electric field is a function of the charge density.
The potential is proportional to the Electric field
The surface charge is:
Usual approach:
VM Ayres, ECE875, S14
Example 01 (will be a continuing problem):
+
VM Ayres, ECE875, S14
Answer:
VM Ayres, ECE875, S14
= 2.32 x 104 cm-3
In forward bias:
= 38.6 V-1 @ r.t.
Example: what is the electron concentration at x = 0?
VM Ayres, ECE875, S14
= 2.32 x 104 cm-3
In forward bias:
= 38.6 V-1 @ r.t.
Answer: need p = p(x)
VM Ayres, ECE875, S14
= 2.32 x 104 cm-3
In forward bias:
= 38.6 V-1 @ r.t.
Can find potential p(at x=0) using strong inversion condition:
2 x Bp =
VM Ayres, ECE875, S14s = p(x=0)
Example:
Evaluate s in strong inversion condition for example problem 01 with NA = 4 x 1015 cm-3
VM Ayres, ECE875, S14
Answer:
VM Ayres, ECE875, S14
p(x = 0) =
Q(x)
E (x)
V (x)
Everything else
To find p(x) (and therefore concentration) must use this approach:
VM Ayres, ECE875, S14
Will get E -field first and also wanted to know that
Metal = battery potential: V
p-type Semiconductor potential: p(x)
New: the potential drop across the (ideal) insulator Vi
Semiconductor surface potential:s = p(x=0)
Electric field and potentials: in inversion:
VM Ayres, ECE875, S14
Breakdown info here concentration info here
VM Ayres, ECE875, S14
LD : the Debye length
VM Ayres, ECE875, S14
Example:
VM Ayres, ECE875, S14
Answer:
VM Ayres, ECE875, S14
Take the square root of E 2 in eq’n 10 and use p(x=0) = s to evaluate:
VM Ayres, ECE875, S14
Can easily find E (x=0) = E s:
VM Ayres, ECE875, S14
Can easily find Q(x=0) = Qs:
Example:
VM Ayres, ECE875, S14
Evaluate Qs for s = 0.67 V
VM Ayres, ECE875, S14
Answer:
VM Ayres, ECE875, S14
VM Ayres, ECE875, S14
VM Ayres, ECE875, S14
s
VM Ayres, ECE875, S14
Note that an important part of the concentration we’d like to know could be defined as charge/area under the Gate (different than usual units)
Example:
VM Ayres, ECE875, S14
Answer:
VM Ayres, ECE875, S14
VM Ayres, ECE875, S14