Keithley 153, Instruction Manual, Page: 19 / 51

APPLI CATIONS
MODEL 153
S E CT I O N 3 . A P P L I CAT I O N S
3 - 1 . G E� ERA L . T h i s
Sec t i on
c o n t a i n s
d e s c r i p t i o n s a n d d i ag ra m s
o f s ome
Ho d e l
1 5 3 a pp l i c a ­
t i o:1 5 .
Th e s e a lo e j u s t s a mp l e s ,
a n d
t h e y d o n o t exhau s t a l l p o s s i b l e u s e s . Re f e r
t o
t h e s e
a p p l i c a t i on s a s d emon s t r a t i o n s
o f
t e c hn iq u e s f o r u s ing t h e Mod e l
1 53 .
3- 2 . NULL DET ECTOR.
a . Th e
Mo d e l
1 5 3
i s
i d e a
l
f o r mo s t nu l l d e t e c t o r a p p l i c a t i on s . I t is p a r t i c u l a r l y u s
e
­
[ u l
for mea s u r i n g sma l l
s i gna l s
f r om
hig h
s ourc e r e s i s t a nc e s . F or
i n s t a nc e , t h e Mo d e l
1 5 3
c a n a c cur a t e l y mea s ur e a l a - m i l l iv o l t s igna l t h r ough a I - megohm s our c e .
b .
F ig u r e 6
s h ows a t y p i c a l nu l l
c i rcu i t
u s ing t h e Le ed s a n d N o r t hrup
K 3
p o t e n t i o me t e r .
T h e Hod e l 1 5 3 i s
c onn e c t ed b e tw e en the unkn own
and
the
potent iometer rather than
a c r o s s
t h e
nu l l
d e t ec t o r
t e rmina l s b e c au s e s hun t s
in
t h e p o t en t i ome t e r r educ e p owe r s en s i t i v i t y .
3 - 3 .
A��ER.
S o l id - s t a t e c
i r
c
u i t d e s ign
o f t en
r eq u i r e s an amme t er w i t h an
e x t r eme ly
wide rang e . F o r examp l e ,
in
t he c i r cu i t o f Figure 7 , g a t e current i s ab ou t
10- 1 1
amp e r e ,
d r a i n current a b o u t 10 - 4 amp ere , b a s e
c
u r r
e
n
t
ab out 3
x
10 - 6 amp e r e , and emi t t e r c
u
r
r
e
n
t
ab ou t 10 - 3 amp e r e . The Mod e l
1 5 3
m
ea s
u
r e
s
the s e curren t s e a s i ly and a c cura t e ly . T h e
l ow vo l t a g e
c ircu i t ry i s
und i s t urbe d b e c au s e t h e Mod e l 1 5 3 h a s a v e ry l ow i n p u t vo l t a g e d r op ,
FIGURE 6 .
Nu l l
Circu i t Us ing
Mod e l
1 5 3
and
Le e d s and
Northrup
K3
Po tent iome t er .
3-4 .
VOLTMETER.
Measuring
microvo l t s
through meg ohm s ourc e r e s i s t a n c e
---
a prime
requ i s i t e
in
s emic onduc t o r r e s i s t iv i t y mea ­
s
u
reme
nt
s -- is
a
s imp l e
t a s k
f o r
the Mod e l
1 5 3 . F igure 8 i l lu s t ra t e s
a
t yp i ca l 4- p o i n t
s emi condu c t o r
r e s i s t ivity
measur ing s ys t em .
Four sharp prob e s
con t a c t
tre
s u r f a c e
of a
s emi c ond u c t o r wa fer o r
ingot . Known
cur­
rent
i s app l i ed through
the
out er two prob e s ,
whi l e the inner two
p ick up
the vo l tag e
drop . Resistivity is
then
computed from
current , v o l tag e d r o p and s pa c ing b e tween
prob e s .
12
FIGURE
7.
Diagram
Showing Curr ents
in
So lid
S ta t e
Circui t s .
:R; 1 153
- . -
we.
FIGURE 8.
Circu i t
Us ing Mod e l 1 5 3 for
S emi c ondu c t or Res i s t ivity Measurement s .