18WuD2x

surface-barrier transistor • surveillance radar 665
Emitter
Collector
surface-barrier transistor
Base
solution are placed on axially opposite points on
the faces of an n-type wafer. At the same time, a
direct current is passed through the wafer and
solution in such a direction as to remove semiconductor
material electrolytically from the faces;
the tiny sprayed areas are etched away. When the
desired wafer thickness is reached at the points
of impact, the etching process is arrested by reversing
the direction of current flow. This reversal
causes an indium dot to be plated on each opposite
face in the etched-out pit. Leads are attached
to the collector and emitter dots and to the wafer
(base).
surface-charge transistor A semiconductor device
consisting essentially of two narrowly separated
plates (source electrode and receiver electrode)
deposited on the film-insulated surface of a silicon
chip, and a third, overlapping electrode (the
transfer gate) deposited on, but insulated from,
the other electrodes. An input signal stores a
charge in the capacitor formed by the source electrode
and chip. A subsequent trigger signal applied
to the transfer gate transfers the charge to
the receiver electrode, where it becomes an output
signal (often amplified, with respect to the input
signal).
surface effect An effect (such as current, resistance,
or resistivity) observed on the surface of a
sample of material, rather than throughout the
body of the material. Compare BULK EFFECT.
surface insulation A coating applied to the surfaces
of core laminations to prevent the passage
of currents between laminations.
surface leakage Leakage of current over the surface
of a dielectric material, as opposed to leakage
through the interior of the material.
surface noise See NEEDLE SCRATCH.
surface recombination rate For a semiconductor,
the rate at which electrons and holes recombine
at the surface. Compare VOLUME RECOMBINA-
TION RATE.
surface resistivity The resistance of a unit area of
a material, measured between opposite edges.
Compare VOLUME RESISTIVITY. Also see RESIS-
TIVITY.
surface tension The tendency of the surface of a
liquid to “shrink.” This property varies with different
liquids and is caused by a net molecular
force directed inward from the surface.
surface wave 1. The earth-guided component of a
ground wave. (The other component is the SPACE
WAVE.) 2. An acoustic wave traveling along the
surface of a plate in a surface-wave amplifier or
surface-wave filter.
surface-wave amplifier An amplifying device consisting
essentially of a surface-wave filter to
which has been added a direct-current-biased n-
type silicon electrode, which is separated from
the crystal substrate of the filter by a very thin
oxide layer. Amplification is produced by interaction
between the electron current in the silicon
and the piezoelectric field of the filter. Also see
ACOUSTOELECTRONICS.
surface-wave filter An acoustoelectronic device
consisting essentially of a crystal plate having
electrodes at each end. An alternating-current
(ac) input signal applied to one electrode sets up
acoustic waves that travel along the surface of the
plate to the other electrode, where they generate
an ac output voltage by piezoelectric action. The
resonant frequency of the device is governed by
the dimensions of the crystal plate. Also see
ACOUSTOELECTRONICS.
surge A sudden rise or flow of current or voltage.
surge absorber See SURGE SUPPRESSOR.
surge arrester See SURGE SUPPRESSOR.
surge current A heavy current that flows initially
into a capacitor when a charging voltage is applied.
surge impedance Symbol, Z o . The impedance seen
by a pulse applied to a transmission line; Z o = L/C
(approximately), where L and C are the inductance
and capacitance, in microhenrys and microfarads,
per unit length of the line. Also called
CHARACTERISTIC IMPEDANCE.
surge protector Misnomer for SURGE SUPPRES-
SOR.
surge suppressor A semiconductor device used to
absorb potentially destructive transients or overvoltages
on a utility power line. It has a three-wire
cord for plugging into a 117-volt outlet, a power
switch, and several three-wire outlets for connection
to sensitive electronic equipment (such as
personal computers, videocassette recorders,
television sets, hi-fi amplifiers, etc.).
surround See SUSPENSION, 1.
Surround Sound The trade name for a multichannel
sound system for use with television receivers
and videocassette players. Some televised movies,
especially on cable and satellite networks, deliver
multichannel sound through receiving/recording
systems equipped with special decoders.
surveillance 1. A method of monitoring a specific
area or volume for intrusion or other disturbance.
2. A means of monitoring a specified portion of
the electromagnetic spectrum for unauthorized
signals.
surveillance radar An air-traffic-control radar that
supplies continuous information regarding the
azimuth and distance of aircraft inside a selected
radius around an airport.