5

Figure 10. Schottky Diode Chip.

Applications Information

Product Selection

Avago’s family of surface mount Schottky diodes provide

unique solutions to many design problems. Each is opti‑

mized for certain applications.

The first step in choosing the right product is to select the

diode type. All of the products in the HSMS‑282x fami‑

ly use the same diode chip–they differ only in package

configuration. The same is true of the HSMS‑280x, ‑281x,

285x, ‑286x and ‑270x families. Each family has a different

set of characteristics, which can be compared most easily

by consulting the SPICE parameters given on each data

sheet.

The HSMS‑282x family has been optimized for use in RF

applications, such as

power monitors) to 4 GHz.

The other feature of the HSMS‑282x family is its unit‑to‑unit

and lot‑to‑lot consistency. The silicon chip used in this se‑

ries has been designed to use the fewest possible process‑

ing steps to minimize variations in diode characteristics.

Statistical data on the consistency of this product, in terms

of SPICE parameters, is available from Avago.

For those applications requiring very high breakdown

voltage, use the HSMS‑280x family of diodes. Turn to the

HSMS‑281x when you need very low flicker noise. The

HSMS‑285x is a family of zero bias detector diodes for small

signal applications. For high frequency detector or mixer

applications, use the HSMS‑286x family. The HSMS‑270x

is a series of specialty diodes for ultra high speed clipping

and clamping in digital circuits.

Schottky Barrier Diode Characteristics

Stripped of its package, a Schottky barrier diode chip con‑

sists of a metal‑semiconductor barrier formed by deposi‑

tion of a metal layer on a semiconductor. The most com‑

mon of several different types, the passivated diode, is

shown in Figure 10, along with its equivalent circuit.

R

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 out‑

put of the diode. C

diode, controlled by the thick‑ness of the epitaxial layer

and the diameter of the Schottky contact. R

tion resistance of the diode, a function of the total current

flowing through it.

On a semi‑log plot (as shown in the Avago 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

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 current, I

height of the diode.

Through the choice of p‑type or n‑type silicon, and the

selection of metal, one can tailor the characteristics of a

Schottky diode. Barrier height will be altered, and at the

same time C

barrier height diodes (with high values of I

zero bias applications) are realized on p‑type silicon. Such

diodes suffer from higher values of R

I

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:

where

n = ideality factor (see table of SPICE parameters)

T = temperature in °K

I

saturation current (see table of SPICE parameters)

I

externally applied bias current in amps

R

the V‑I curve

METAL

SCHOTTKY JUNCTION

PASSIVATION

PASSIVATION

N-TYPE OR P-TYPE EPI LAYER

N-TYPE OR P-TYPE SILICON SUBSTRATE

CROSS-SECTION OF SCHOTTKY

BARRIER DIODE CHIP

EQUIVALENT

CIRCUIT

0.026

≈ ––––– at 25 °C

–––––

– 1)

0.026

0.026

≈ ––––– at 25 °C

–––––

– 1)

0.026