Surface Mount Zero Bias
Schottky Detector Diodes
Technical Data
HSMS-285x Series
Features
• Surface Mount SOT-23/
SOT-143 Packages
• Miniature SOT-323 and
SOT-363 Packages
• High Detection Sensitivity:
up to 50 mV/µW at 915 MHz
• Low Flicker Noise:
-162 dBV/Hz at 100 Hz
• Low FIT (Failure in Time)
Rate*
• Tape and Reel Options
Available
• Matched Diodes for
Consistent Performance
• Better Thermal
Conductivity for Higher
Power Dissipation
• Lead-free Option Available
* For more information see the Surface
Mount Schottky Reliability Data Sheet.
SOT-23/SOT-143 Package
Lead Code Identification
(top view)
SINGLE
3
SERIES
3
Description
Agilent’s HSMS-285x family of
zero bias Schottky detector
diodes has been designed and
optimized for use in small signal
(P
in
< -20 dBm) applications at
frequencies below 1.5 GHz. They
are ideal for RF/ID and RF Tag
applications where primary (DC
bias) power is not available.
Important Note:
For detector
applications with input power
levels greater than –20 dBm, use
the HSMS-282x series at frequen-
cies below 4.0 GHz, and the
HSMS-286x series at frequencies
above 4.0 GHz. The HSMS-285x
series IS NOT RECOMMENDED
for these higher power level
applications.
Available in various package
configurations, these detector
diodes provide low cost solutions
to a wide variety of design prob-
lems. Agilent’s manufacturing
techniques assure that when two
diodes are mounted into a single
package, they are taken from
adjacent sites on the wafer,
assuring the highest possible
degree of match.
1
#0
2
1
#2
2
UNCONNECTED
PAIR
3
4
1
#5
2
SOT-323 Package Lead
Code Identification
(top view)
SINGLE
3
SERIES
3
Pin Connections and
Package Marking
1
2
3
6
5
4
1
B
2
1
C
2
SOT-363 Package Lead
Code Identification
(top view)
UNCONNECTED
TRIO
6
5
4
6
Notes:
1. Package marking provides orienta-
tion and identification.
2. See “Electrical Specifications” for
appropriate package marking.
PLx
BRIDGE
QUAD
5
4
1
2
L
3
1
2
P
3
5
Applications Information
Introduction
Agilent’s HSMS-285x family of
Schottky detector diodes has been
developed specifically for low
cost, high volume designs in small
signal (P
in
< -20 dBm) applica-
tions at frequencies below
1.5 GHz. At higher frequencies,
the DC biased HSMS-286x family
should be considered.
In large signal power or gain con-
trol applications (P
in
> -20 dBm),
the HSMS-282x and HSMS-286x
products should be used. The
HSMS-285x zero bias diode is not
designed for large signal designs.
Schottky Barrier Diode
Characteristics
Stripped of its package, a
Schottky barrier diode chip
consists of a metal-semiconductor
barrier formed by deposition of a
metal layer on a semiconductor.
The most common of several
different types, the passivated
diode, is shown in Figure 5, along
with its equivalent circuit.
tance of the diode, controlled by
the thickness of the epitaxial layer
and the diameter of the Schottky
contact. R
j
is the junction
resistance of the diode, a function
of the total current flowing
through it.
8.33 X 10
-5
n T
R
j
= –––––––––––– = R
V
– R
s
I
S
+ I
b
0.026
= ––––– at 25°C
I
S
+ I
b
where
n = ideality factor (see table of
SPICE parameters)
T = temperature in
°K
I
S
= saturation current (see
table of SPICE parameters)
I
b
= externally applied bias
current in amps
I
S
is a function of diode barrier
height, and can range from
picoamps for high barrier diodes
to as much as 5
µA
for very low
barrier diodes.
The Height of the Schottky
Barrier
The current-voltage characteristic
of a Schottky barrier diode at
room temperature is described by
the following equation:
V - IR
S
I = I
S
(exp –––––– - 1)
0.026
current, I
S
, and is related to the
barrier height of the diode.
Through the choice of p-type or
n-type silicon, and the selection of
metal, one can tailor the charac-
teristics of a Schottky diode.
Barrier height will be altered, and
at the same time C
J
and R
S
will be
changed. In general, very low
barrier height diodes (with high
values of I
S
, suitable for zero bias
applications) are realized on
p-type silicon. Such diodes suffer
from higher values of R
S
than do
the n-type. Thus, p-type diodes are
generally reserved for small signal
detector applications (where very
high values of R
V
swamp out high
R
S
) and n-type diodes are used for
mixer applications (where high
L.O. drive levels keep R
V
low).
Measuring Diode Parameters
The measurement of the five
elements which make up the low
frequency equivalent circuit for a
packaged Schottky diode (see
Figure 6) is a complex task.
Various techniques are used for
each element. The task begins
with the elements of the diode
chip itself.
C
P
N-TYPE OR P-TYPE SILICON SUBSTRATE
;;
METAL
PASSIVATION
N-TYPE OR P-TYPE EPI
R
S
PASSIVATION
LAYER
SCHOTTKY JUNCTION
C
j
R
j
(
)
L
P
EQUIVALENT
CIRCUIT
R
V
R
S
C
j
CROSS-SECTION OF SCHOTTKY
BARRIER DIODE CHIP
Figure 5. Schottky Diode Chip.
R
S
is the parasitic series
resistance of the diode, the sum of
the bondwire and leadframe
resistance, the resistance of the
bulk layer of silicon, etc. RF
energy coupled into R
S
is lost as
heat — it does not contribute to
the rectified output of the diode.
C
J
is parasitic junction capaci-
On a semi-log plot (as shown in
the Agilent catalog) the current
graph will be a straight line with
inverse slope 2.3 X 0.026 = 0.060
volts per cycle (until the effect of
R
S
is seen in a curve that droops
at high current). All Schottky
diode curves have the same slope,
but not necessarily the same value
of current for a given voltage. This
is determined by the saturation
FOR THE HSMS-285x SERIES
C
P
= 0.08 pF
L
P
= 2 nH
C
j
= 0.18 pF
R
S
= 25
Ω
R
V
= 9 KΩ
Figure 6. Equivalent Circuit of a
Schottky Diode.
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