1 2
ton approach, is provided together with an increase in
OPTOMICROWAVE INTEGRATED CIRCUIT switching speed, as only a single light beam is required
for on-off switching, with the device itself being formed
FIELD OF THE INVENTION of a thin active semiconductor layer as opposed to a
The present invention relates to the field of semicon- 5 relatively thick bulk material as in the Auston switch,
ductor apparatus and, more particularly, to optically The isolation may take the form of a narrow ribbon of
controlled semiconductor devices for switching or conductive material disposed on the surface of the thin
modifying electrical signals, especially microwave sig- active layer at the gap between separated ends of the
nals. microstrip. This narrow ribbon is connected to a bias
10 potential (e.g. ground), to create an isolation-enhancing
BACKGROUND OF THE INVENTION depletion region in that portion of the active layer di
Over the last two decades, the electronics industry rectly beneath the narrow ribbon. The thus generated
has witnessed rapid development and expansion of new depletion region provides input/output isolation in the
devices and entire technologies evolving from the de- gap between the separated ends of the microstrip.
vices themselves. For example, efforts to reduce cost, 15 To turn the switch on, the gap is illuminated with a
size, power consumption, and improve on speed, band- beam of light, in response to which electron-hole pairs
width, isolation, etc., of components and systems have in the semiconductor material of the active layer are
resulted in the development of integrated circuits and generated, from the valence to the conduction band,
their evolution into LSI, VLSI, and IOC (integrated This generation of electron-hole pairs increases the
optic circuits), the latter employing optical dielectric 20 carrier concentration, reduces the cross-sectional area
waveguides. 0f the depletion region and increases current flow in the
Within this sector of component development, a gapj so tnat the separated ends of the microstrip are
number of optically responsive devices, such as light effectively electrically connected. To turn the device
controlled switching devices (e.g. thyristors, optically off> the beam of light is extinguished, cancelling the
response FETs, etc.) have been proposed. One such 25 ... generated carrier and restoring the isoiating de.
switch device which is purported to have particular pietion region
utility in switching signals at microwave frequencies is In lace Qf the exclusive use of a generated narrow
described >n the U.S. patent to Auston, U.S. Pat. No. ribbon in ^ gap for input/output isolation> the switch
.lL , , , . . , • -m device of the present invention may be configured so
In accordance with the proposed device, a microstrip -JO , , r ■ u c • * • ■ r ,l
_ . . K y . ' , . lL ^ that, near the gap, each section of microstrip is further
configuration having a gap in a conductive strip that . • * J J J •
r °., . • ° r. , .. , ... r . , interrupted having a pair separated and ad acent nar
forms the signal carrying path is selectively illuminated , . . '° ^ K . \. . ,. , J
by a first beam of light for temporarily providing a high row f>P« the extent or length of which are a quarter
electrical conductivity region in the surface of the semi- wavelength of the microwave frequency to be carried
conductor bulk material between separated ends of the 35 °ver thf m.crostr.p. That section of the microstrip de
conductive strip, whereby the device is effectively fln,nS the SaP 18 cou?'fd vla a ^aTter wavelength ter
turned-on, providing a signal carrying path through the ""nation stnp to whlch a DC blas voItage ls apphed)
conductive strip and the illuminated surface of the semi- thereby Providing signal level compensation and R.F.
conductor bulk at the gap in the strip. To turn the de- isolation between separated sections of the microstrip.
vice off, a second beam of light, to which the bulk re- 40 In a further embodiment of the switch, both the m
sponds, must be directed at the device, creating an ef- put/isolation-providing grounded ribbon and the R.F.
fective short circuit from the conductive strip, through isolation sections may be provided for enhanced isola
the bulk itself, to a ground plane disposed on the bulk tion between opposite ends of the strip.
material „ BRIEF DESCRIPTION OF THE DRAWINGS
Unfortunately, because of its configuration and mode 45
of operation, this device requires considerable driving FIG. 1 is a plan view of a first embodiment of an
power (on the order of several watts) to trigger the optically controlled microwave switch in accordance
switch, is subject to cross talk problems and has limited with the present invention;
bandwidth (as separate switching control signals are FIG- 2 is a sectional view of a microwave switch
required for turning the switch on and off). 50 taken along line I—I of FIG. 1;
FIG. 3 is a plan view of a second embodiment of an
SUMMARY OF THE INVENTION optically controlled microwave switch according to the
In accordance with the present invention, there is present invention; and
provided a new and improved optically responsive FIG. 4 is a plan view of a third embodiment of an
integrated circuit device especially useful for micro- 55 optically controlled microwave switch according to the
wave signalling/switching applications. In one embodi- present invention.
ment of the inventive optically controlled microwave DETAILED DESCRIPTION switch, a microstrip structure is formed on a thin layer
of active semiconductor material, such as doped GaAs Referring now to FIGS. 1 and 2, there are illustrated
or silicon, that is disposed atop an insulator substrate. 60 respective plan and sectional views of a first embodi
Like the conductor highway structure of the device ment of the present invention. The sectional view in
described in the above-referenced patent to Auston, FIG. 2 is taken along line I—I of FIG. 1. The optically
there is a gap formed in the conductive strip and radiant controlled microstrip switch in the present embodiment
energy is directed onto the exposed surface of the active comprises a microstripline conductor layer 10 disposed
layer therebeneath for the purpose of bridging the gap 65 on the surface of a thin active semiconductor layer 14
via a surface-generated charge carrier region. How- which, in turn, is disposed upon an insulator substrate
ever, here the similarity ends. Pursuant to the present 15. Microstrip conductor 10 is spaced apart from an
invention, electrical isolation, not afforded by the Aus- other signal microstrip conductor layer 13 also disposed
