U.S. patent application number 13/029951 was filed with the patent office on 2012-08-23 for optocoupler circuit.
Invention is credited to Dusan Golubovic, Gerhard Koops, Rob Van Dalen, Tony Vanhoucke.
Application Number | 20120213466 13/029951 |
Document ID | / |
Family ID | 45655713 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120213466 |
Kind Code |
A1 |
Golubovic; Dusan ; et
al. |
August 23, 2012 |
Optocoupler Circuit
Abstract
An optocoupler device facilitates on-chip galvanic isolation. In
accordance with various example embodiments, an optocoupler circuit
includes a silicon-on-insulator substrate having a silicon layer on
a buried insulator layer, a silicon-based light-emitting diode
(LED) having a silicon p-n junction in the silicon layer, and a
silicon-based photodetector in the silicon layer. The LED and
photodetector are respectively connected to galvanically isolated
circuits in the silicon layer. A local oxidation of silicon (LOCOS)
isolation material and the buried insulator layer galvanically
isolate the first circuit from the second circuit to prevent charge
carriers from moving between the first and second circuits. The LED
and photodetector communicate optically to pass signals between the
galvanically isolated circuits.
Inventors: |
Golubovic; Dusan; (Leuven,
BE) ; Koops; Gerhard; (Aalst, BE) ; Vanhoucke;
Tony; (Bierbeek, BE) ; Van Dalen; Rob;
(Bergeijk, NL) |
Family ID: |
45655713 |
Appl. No.: |
13/029951 |
Filed: |
February 17, 2011 |
Current U.S.
Class: |
385/14 ;
257/E31.109; 438/24 |
Current CPC
Class: |
H01L 27/15 20130101;
H01L 33/343 20130101; H01L 31/173 20130101 |
Class at
Publication: |
385/14 ; 438/24;
257/E31.109 |
International
Class: |
G02B 6/122 20060101
G02B006/122; H01L 31/18 20060101 H01L031/18 |
Claims
1. An integrated optocoupler circuit comprising: a
silicon-on-insulator substrate having a silicon layer on a buried
insulator layer; first and second circuits located in the silicon
layer and respectively operating at voltages that are at least an
order of magnitude different from one another; an insulator in a
portion of the silicon layer, the insulator and the buried
insulator layer being configured to galvanically isolate the first
circuit from the second circuit; and an optocoupler including a
transmitter circuit electrically connected to one of the first and
second circuits, and configured to transmit an optical signal based
upon an electrical signal received from the one of the first and
second circuits, and a receiver circuit electrically connected to
the other one of the first and second circuits, and configured to
receive the optical signal communicated from the transmitter
circuit and to communicate an electrical signal to the other one of
the first and second circuits, based upon the received optical
signal.
2. The circuit of claim 1, wherein the insulator and the buried
insulator layer are configured to galvanically isolate the first
circuit from the second circuit by preventing charge carriers from
moving between circuits.
3. The circuit of claim 1, further including a second transmitter
circuit electrically connected to the other one of the first and
second circuits, and configured to transmit an optical signal based
upon an electrical signal received from the other one of the first
and second circuits, and a second receiver circuit electrically
connected to the one of the first and second circuits, and
configured to receive the optical signal communicated from the
second transmitter circuit and to communicate an electrical signal
to the one of the first and second circuits, based upon the
received optical signal.
4. The circuit of claim 1, wherein one of the first and second
circuits operates at a high voltage, the other one of the first and
second circuits operates at a low voltage and is susceptible to
circuit damage upon exposure to the high voltage, and the insulator
is configured to galvanically isolate the other one of the first
and second circuits from the high voltage.
5. The circuit of claim 1, wherein the semiconductor substrate is a
silicon-on-insulator substrate having a silicon layer on a buried
insulator layer, the first circuit, the second circuit and the
optocoupler are formed in at least a portion of the silicon layer,
and said insulator and an insulator layer of the
silicon-on-insulator substrate galvanically isolate the first and
second circuits from one another.
6. The circuit of claim 1, wherein the semiconductor substrate is a
silicon-on-insulator substrate having a silicon layer on a buried
insulator layer, the silicon layer being sufficiently thin to
mitigate the acceleration of charge carriers between upper and
lower surfaces of the silicon layer to an energy level at which
avalanche breakdown occurs, the first circuit, the second circuit
and the optocoupler being formed in at least a portion of the
silicon layer, and said insulator and an insulator layer of the
silicon-on-insulator substrate galvanically isolate the first and
second circuits from one another.
7. The circuit of claim 1, wherein the insulator includes a local
oxidation of silicon (LOCOS) isolation material that includes an
oxidized portion of a silicon layer in which the first and second
circuits are formed, that galvanically isolates the first and
second circuits from one another.
8. The circuit of claim 1, wherein the insulator includes a local
oxidation of silicon (LOCOS) isolation material that is configured
to galvanically isolate the first and second circuits from one
another under conditions in which one of the circuits operates at a
voltage of at least about 2000 V.
9. The circuit of claim 1, wherein the semiconductor substrate is a
silicon-on-insulator substrate having a silicon layer on a buried
insulator layer, the first circuit, the second circuit and the
optocoupler are formed in at least a portion of the silicon layer,
and the insulator includes a local oxidation of silicon (LOCOS)
isolation material in the silicon layer, the thickness of the LOCOS
material being the same as the thickness of the buried insulator
layer.
10. The circuit of claim 1, wherein the transmitter circuit
includes a silicon-based light emitting diode, and the receiver
includes a silicon-based photodetector.
11. The circuit of claim 1, wherein the transmitter and receiver
circuits include implanted portions of a silicon layer of a
silicon-on-insulator substrate, and the insulator galvanically
isolates the respective implanted portions of the silicon layer
that form the transmitter and receiver circuits.
12. The circuit of claim 1, wherein the transmitter circuit
includes a silicon-based light-emitting diode having a silicon p-n
junction with a bandgap modified for operation in a forward-biased
state.
13. The circuit of claim 1, wherein the transmitter circuit
includes a silicon-based light-emitting diode having a silicon p-n
junction configured to operate in a forward-biased state, and
having a bandgap modified by silicon nitride deposited via
plasma-enhanced chemical vapor deposition.
14. The circuit of claim 1, wherein the transmitter circuit
includes a silicon-based light-emitting diode having a silicon p-n
junction configured to operate in a forward-biased state, further
comprising a silicon nitride material configured to modify the
bandgap of the p-n junction to operate the p-n junction in a
forward-biased state.
15. The circuit of claim 1, wherein the transmitter circuit
includes a silicon-based light-emitting diode having a silicon p-n
junction configured to operate in a forward-biased state, and
dislocation loops on one side of the p-n junction that modify the
bandgap of the p-n junction.
16. An optocoupler circuit comprising: a silicon-on-insulator
substrate having a silicon layer on a buried insulator layer; a
silicon-based light-emitting diode (LED) having a silicon p-n
junction in the silicon layer and connected to a first circuit in
the silicon layer, the silicon p-n junction being configured to
operate in a forward-biased state; a silicon-based photodetector in
the silicon layer and connected to a second circuit in the silicon
layer; a local oxidation of silicon (LOCOS) isolation material that
includes an oxidized portion of the silicon layer, the LOCOS
isolation material and the buried insulator layer being configured
to galvanically isolate the first circuit from the second circuit
to prevent charge carriers from moving between the first and second
circuits; and a waveguide optically coupling the LED and
photodetector for passing an optical signal from the LED to the
photodetector to facilitate communications between the
galvanically-isolated first and second circuits.
17. The circuit of claim 16, further including silicon nitride
material adjacent the p-n junction and configured to modify the
bandgap of the p-n junction.
18. A method for manufacturing an optocoupler device on a
silicon-on-insulator (SOI) substrate having a silicon layer on a
buried insulator, the method comprising: forming a silicon-based
light-emitting diode (LED) having a silicon p-n junction in the
silicon layer and connected to a first circuit in the silicon
layer, the silicon p-n junction being configured to operate in a in
a forward-biased state; forming a silicon-based photodetector in
the silicon layer and connected to a second circuit in the silicon
layer; oxidizing a portion of the silicon layer using a local
oxidation of silicon (LOCOS) process to form a LOCOS insulation
material configured, with the buried insulator layer, to
galvanically isolate the first circuit from the second circuit to
prevent charge carriers from moving between the first and second
circuits; forming a waveguide optically coupling the LED and
photodetector for passing an optical signal from the LED to the
photodetector to facilitate communications between the
galvanically-isolated first and second circuits.
19. The method of claim 18, wherein forming a silicon-based LED
includes depositing silicon nitride material at the p-n junction
via plasma-enhanced chemical vapor deposition to modify the bandgap
of the LED to configure the LED to operate in a forward-biased
state.
20. The method of claim 18, wherein forming a silicon-based LED
includes forming dislocation loops at a p-n junction of the LED to
modify the bandgap of the p-n junction and configure the p-n
junction to operate in a forward-biased state.
Description
[0001] Various aspects of the present invention are directed to
electronic circuits, and more particularly to monolithically
integrated optocoupler circuits.
[0002] A variety of circuit devices employ isolation for a variety
of purposes. One example type of circuit isolation is galvanic
isolation, which allows the exchange of information between two
parts of an electric circuit or two electric circuits without the
actual flow of charge carriers between them. Galvanic isolation has
been used in a variety of circuits, including those having
different parts that operate at significantly different voltages in
order to protect a lower voltage part, avoid unwanted ground loop
bias, and achieve other desirable characteristics.
[0003] One type of galvanic isolation circuit is an optocoupler
circuit, or chip. Generally, an optocoupler has a light emitting
photodiode and a photodetector separated by a transparent
dielectric layer. To achieve galvanic isolation using such an
approach, optocoupler circuits are often combined with other chips
in a package. However, such approaches may not be suitable for many
applications for a variety of reasons. For example, such an
arrangement may be susceptible to undesirable signal delays due to
the paths via which the signals must traverse. In addition, such
devices can be relatively complex as well as added complexity/cost
associated with interfacing transmitters and receivers via the
optocoupler.
[0004] Accordingly, the implementation of circuits requiring
electrical and/or galvanic isolation continues to be
challenging.
[0005] Various example embodiments are directed to optocoupler
circuits for a variety of applications and addressing various
challenges, including those discussed above.
[0006] According to an example embodiment, an optocoupler circuit
includes a silicon-on-insulator substrate having a silicon layer on
a buried insulator layer, and first and second circuits located in
the silicon layer and respectively operating at voltages that are
at least an order of magnitude different from one another. An
insulator is located in a portion of the silicon layer and, with
the buried insulator layer, galvanically isolates the first circuit
from the second circuit. An optocoupler includes transmitter and
receiver circuits in the silicon layer. The transmitter circuit is
electrically connected to one of the first and second circuits, and
transmits an optical signal based upon an electrical signal
received from the one of the first and second circuits. The
receiver circuit is electrically connected to the other one of the
first and second circuits, and receives the optical signal
communicated from the transmitter circuit, and communicates an
electrical signal to the other one of the first and second circuits
based upon the received optical signal.
[0007] Another example embodiment is directed to an optocoupler
circuit having a silicon-on-insulator substrate with a silicon
layer on a buried insulator layer, a silicon-based light-emitting
diode (LED) and a silicon-based photodetector. The LED has a
silicon p-n junction in the silicon layer and connected to a first
circuit in the silicon layer, with the silicon p-n junction being
configured to operate in a forward-biased state. The silicon-based
photodetector is also located in the silicon layer and is connected
to a second circuit in the silicon layer. A local oxidation of
silicon (LOCOS) isolation material includes an oxidized portion of
the silicon layer, and is configured with the buried insulator
layer to galvanically isolate the first circuit from the second
circuit to prevent charge carriers from moving therebetween. A
waveguide optically couples the LED and photodetector for passing
an optical signal from the LED to the photodetector to facilitate
communications between the galvanically-isolated first and second
circuits.
[0008] Another example embodiment is directed to a method for
manufacturing an optocoupler device on a silicon-on-insulator (SOI)
substrate having a silicon layer on a buried insulator. A
silicon-based light-emitting diode (LED) having a silicon p-n
junction is formed in the silicon layer and connected to a first
circuit in the silicon layer, the silicon p-n junction being
configured to operate in a forward-biased state. A silicon-based
photodetector is also formed in the silicon layer and connected to
a second circuit in the silicon layer. A portion of the silicon
layer is oxidized using a local oxidation of silicon (LOCOS)
process to form a LOCOS insulation material that, with the buried
insulator layer, galvanically isolates the first circuit from the
second circuit to prevent charge carriers from moving between the
first and second circuits. A waveguide is formed optically coupling
the LED and photodetector for passing an optical signal from the
LED to the photodetector to facilitate communications between the
galvanically-isolated first and second circuits.
[0009] The above discussion is not intended to describe each
embodiment or every implementation of the present disclosure. The
figures and following description also exemplify various
embodiments.
[0010] Various example embodiments may be more completely
understood in consideration of the following detailed description
in connection with the accompanying drawings, in which:
[0011] FIG. 1 shows an optocoupler having light emitting diode
(LED) and photodetector, according to an example embodiment of the
present invention;
[0012] FIG. 2 shows an optocoupler at a first stage of manufacture,
with an SOI wafer and a buried oxide (BOX) covered with a hard
mask, according to another example embodiment of the present
invention;
[0013] FIG. 3 shows an optocoupler at another stage of manufacture,
involving a photo step that defines SOI areas to be exposed to
LOCOS (local oxidation of silicon) oxidation, according to another
example embodiment of the present invention;
[0014] FIG. 4 shows an optocoupler at another stage of manufacture,
in which a hard mask is removed by dry etching areas to be
oxidized, according to another example embodiment of the present
invention;
[0015] FIG. 5 shows an optocoupler at another stage of manufacture,
in which thermal oxide is locally grown using a LOCOS process on a
SOI wafer to merge with an underlying BOX, according to another
example embodiment of the present invention;
[0016] FIG. 6 shows a top view of an optocoupler, according to
another example embodiment of the present invention; and
[0017] FIG. 7 shows another top view of an optocoupler, according
to another example embodiment of the present invention.
[0018] While the invention is amenable to various modifications and
alternative forms, specifics thereof have been shown by way of
example in the drawings and will be described in detail. It should
be understood, however, that the intention is not to limit the
invention to the particular embodiments described. On the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the scope of the invention including
aspects defined in the claims. Furthermore, the term "example" as
used throughout this document is by way of illustration, and not
limitation.
[0019] The present invention is believed to be applicable to a
variety of different types of circuits, devices and arrangements
involving optocouplers. While the present invention is not
necessarily limited in this context, various aspects of the
invention may be appreciated through a discussion of various
related examples.
[0020] According to an example embodiment, an optocoupler is
incorporated on a single integrated circuit chip, for optically
communicating between electrically isolated circuits in the chip.
The optocoupler includes an optical transmitter and an optical
receiver that optically communicate with one another and
respectively communicate with different ones of the electrically
isolated circuits. This optical communication facilitates
communications between the electrically isolated circuits.
[0021] Another example embodiment is directed to an optocoupler
circuit in which a transmitter and a receiver (or transceivers) are
connected to electrically isolated circuits in an integrated
circuit chip. The optocoupler circuit facilitates optical
communications between the isolated circuits, while electrical
isolation between the isolated circuits is maintained.
[0022] The transmitters and receivers as discussed above are
respectively connected to electrical circuits in the chip,
communicate with the electrical circuit connected thereto, and
further communicate signals sent to and/or received from another
receiver, transmitter or transceiver. The optocoupler and/or other
portions of the chip generate optical signals based on electrical
signals for transmission, and generate electrical signals based on
optical signals for reception. Accordingly, the integrated circuit
portions that are electrically isolated from one another may
communicate with one another via an optical communication path,
while maintaining electrical isolation. In addition, the respective
circuit portions and optical transmitter/receiver/transceiver may
be fabricated on a common chip (e.g., with one or more components
formed simultaneously), which can be beneficial for a variety of
implementations, such as to facilitate the combination of
manufacturing steps, reduction of cost, or simplification of
products.
[0023] Another example embodiment is directed to a method for
manufacturing an optocoupler device. Separate circuits are formed
in disparate portions of a semiconductor chip. An optocoupler
transmitter is connected to one of the circuits, and an optocoupler
receiver is connected to the other one of the integrated circuits.
An electrical isolation material is formed to electrically isolate
the separate circuits from one another, and also to electrically
insulate the optocoupler transmitter and receiver. An optical
conduit or medium may optionally be formed to facilitate optical
coupling of the transmitter and receiver.
[0024] The various embodiments discussed herein are applicable to
implementation in a variety of manners. In some embodiments, the
optocoupler device is formed in a silicon layer of a
silicon-on-insulator (SOI) wafer. A buried oxide layer (the
insulator portion of the SOI wafer) is formed having a thickness to
suitably provide electrical isolation as discussed herein. For
example, an oxide thickness of about 1 .mu.m can be used to provide
on-chip isolation for 500 V operation, and an oxide thickness of
about 4 .mu.m can be used to provide on-chip isolation for 2000V
operation. In other embodiments, an optocoupler as discussed herein
is implemented using the A-BCD (Advanced Bipolar-CMOS-DMOS) or the
EZ-HV wafer (and process for the production of commercial
high-voltage silicon-on-insulator (HV-SOI) ICs)), available from
NXP Semiconductors of Eindhoven, The Netherlands. Such approaches
can be implemented, for example, to incorporate high-voltage
circuits that can handle rectified AC line supply voltages, as well
as low-voltage CMOS logic to provide on-chip intelligence.
[0025] In some implementations, the silicon layer of the SOI wafer
has a thickness that mitigates avalanche breakdown. For example, by
limiting the thickness to one micron or a few microns, the ability
of charge carriers in the silicon layer to accelerate to an energy
at which avalanche breakdown occurs is inhibited. Using this
approach together with the integrated optocoupler and circuit
isolation within the silicon layer and via the underlying buried
insulator, a circuit operating at high voltage can be integrated
and isolated from circuits operating at lower voltage.
[0026] In connection with various example embodiments, an
optocoupler circuit such as described herein includes an insulating
material that is used to galvanically isolate integrated circuits
fabricated using silicon-on-insulator (SOI) wafers (e.g., for
operation at voltage ranges up to 2000V). The SOI device can be
implemented in vehicle-type communications systems such as the
local interconnect network (LIN) or the controller-area network
(CAN) as standalone transceivers, as well as LIN/CAN system basis
chips (e.g., with communication data rate that do not exceed 20-30
Mbps).
[0027] As commensurate with various example embodiments, an
insulator as discussed herein is configured to galvanically isolate
circuits by preventing charge carriers from moving between
circuits. In many embodiments, the grounds of each of the
galvanically isolated circuits are at different potentials. The
respective isolated circuits can be operated at potentials that are
an order of magnitude different than one another.
[0028] Electrical (e.g., galvanic) isolation between disparate
portions of a chip communicatively coupled via an optocoupler is
effected using one or more of a variety of approaches. In some
implementations, LOCOS (local oxidation of silicon) isolation is
used in connection with the buried oxide to achieve full dielectric
isolation of the respective circuit portions. The width, thickness
and other characteristics of the LOCOS are set to suit particular
applications. In some implementations, the width of the LOCOS is
set to about 4 .mu.m wide for application with voltages of 2000V
(e.g., as commensurate with the above-referenced example thickness
of the buried oxide in the SOI structure). In certain
implementations, the thickness of LOCOS t.sub.LI is determined by
the selected thickness of the SOL as back-end-of-line isolation
layers, used for the formation of metallization, are used to attain
sufficient dielectric isolation.
[0029] Communication circuits used in connection with the
optocouplers as discussed herein may include one or more of a
variety of components. In some embodiments, a photodiode,
photodetector and optical waveguide are implemented using planar
silicon-based fabrication technology, to respectively form a
transmitter, receiver and optical link for the optocoupler. As
other examples, transmitters such as a laser, light-emitting diode
(LED), or other light-producing circuit can be used. Similarly,
light receivers may employ circuits such as a photo multiplier
tube, photo transistor or avalanche photodiode to detect light.
Various embodiments are directed to a transmitter/receiver
combination of silicon-based light emitting diodes and
photodetectors. Optical links such as a fiber optic cable,
waveguide, or a medium such as air or other fluid may be used as
the optical waveguide.
[0030] In some embodiments, an optical receiver as discussed herein
includes a p-i-n photodetector implemented using implants in a CMOS
process. For instance, a photodiode can be implemented using
n+/n-well/p-substrate or p+/n-well/p-substrate, such as used in
CMOS image sensors. Implant layers used in other standard CMOS
processes can also be used.
[0031] A silicon-based LED is used as an optical transmitter in
various embodiments, with the optocoupler circuit configured to
stress a silicon p-n junction in the LED to modify the bandgap,
facilitating efficient light generation in a forward-biased
operation mode. In some implementations, the stress is realized by
using plasma-enhanced chemical vapor deposition of silicon nitride,
or by intentionally inducing dislocation loops on one side of the
p-n junction of the LED. This approach can be used to mitigate
efficiency issues with such diodes as related to an indirect
bandgap, as well as high free carrier absorption.
[0032] In some implementations, a waveguide used to optically link
the transmitter and receiver portions of an optocoupler as
discussed herein includes a silicon nitride material having a
relatively high refractive index (e.g., n.sub.SiN.apprxeq.2), to
facilitate total (or near total) internal reflection. Light
transmitted from the transmitter (e.g., an LED) into the waveguide
can be efficiently confined in the waveguide and transmitted to the
receiver (e.g., a photodetector) without significant losses.
Moreover, due to the confinement of light in the waveguide, adverse
effects such as those associated with on-chip emitted radiation can
be mitigated or otherwise minimized.
[0033] Turning now to the Figures, FIG. 1 shows an optocoupler
circuit 100, in accordance with another example embodiment. The
optocoupler circuit 100 includes a silicon-on-insulator structure
including a silicon layer 110 on a buried insulator 120, over a
silicon substrate 130. A photodiode 140 (e.g., a light emitting
diode (LED)) and photodetector 150 are formed in the silicon layer
110, and separated by a LOCOS insulator 160. The photodiode 140 and
photodetector 150 respectively have p-n junctions 142 and 152 via
which light is generated from an electrical input, and via which an
electrical output is generated from light. Light is passed from the
photodiode 140 to the photodetector 150 through a waveguide type of
material 170. The LOCOS 160 and the buried insulator 120 serve to
galvanically isolate the respective circuit portions of the
photodiode 140 and photodetector 150, and other circuitry connected
thereto (e.g., at laterally adjacent portions of the silicon layer
110). In this context, high voltage circuits on one side of the
LOCOS 160 (e.g., at the photodetector 150) can be galvanically
isolated from lower voltage circuits operating at another side of
the LOCOS 160 (e.g., at photodiode 140). Voltages of an order of
magnitude (or more) in difference can be electrically, and
galvanically, isolated in this manner.
[0034] The photodiode 140 and photodetector 150 can be formed using
one or more of a variety of approaches, to suit different
applications. For example, implantations of doping species such as
Boron, Arsenic, and Phosphorous can be used to form the respective
photodiode/photodetector pair 140 and 150, and respective p-n
junctions. The implantations can be done specifically to form the
photodiode 140 and photodetector 150, or as part of available
implantation conditions used for the fabrication of surrounding
integrated circuits. The implant materials and related approach can
be implemented to achieve desired properties of the photodiode and
photodetector, as well as upon the implant availability in the
selected process platform.
[0035] The waveguide 170 can also be formed using one or more of a
variety of materials that facilitate the communication of optical
signals between the photodiode 140 and photodetector 150. In some
implementations, the waveguide 170 is a silicon nitride (SiN)
material formed on the LOCOS 160 to optically connect the
photodiode 140 and photodetector 150. The optically active
junctions 142 and 152 are offset from the edge of the LOCOS
isolation 160 to reduce, or minimize, the influence of defects
formed during a heavy thermal oxidation.
[0036] In some implementations, the SiN waveguide 170 is used as a
stress layer to modify the bandgap of the photodiode 140, to
achieve efficient light generation in a forward-biased operation
mode. In other implementations, an additional SiN layer can be
deposited at the photodetector 140 to achieve bandgap
modification.
[0037] FIGS. 2-5 show an optocoupler circuit 200 at various stages
of manufacture, in accordance with other example embodiments. The
optocoupler circuit 200 and related approaches described herein
may, for example, be used to form the optocoupler circuit 100 shown
in FIG. 1. In this context, FIGS. 2-5 use reference numbers that
are similar to those used in FIG. 1 (e.g., buried oxide layer 220
in FIG. 2 is labeled similarly to 120 and 220), for
illustration.
[0038] Referring to FIG. 2, an optocoupler 200 is shown at a first
stage of manufacture, with an SOI wafer having a silicon layer 210
on a buried oxide (BOX) layer 220, over a substrate 230 (e.g.,
silicon), in accordance with another example embodiment of the
present invention. The silicon layer 210 is covered with a hard
mask 280, including materials such as a thin silicon pad-oxide (at
the interface with the silicon layer 210) and silicon nitride. The
thickness of hard mask 280 and layers (e.g., SiN) therein are set
to provide protection of the underlying silicon layer 210 against
thermal oxidation. The thickness of the buried oxide 220,
represented by arrows as t.sub.Box, can be set to achieve desired
galvanic isolation of separated circuit portions, in a manner as
discussed elsewhere herein.
[0039] FIG. 3 shows an optocoupler 300 at another stage of
manufacture, in connection with another example embodiment. A photo
resist layer 290 has been formed on hard mask layer 280 and over an
underlying SOI wafer, such as shown in FIG. 2. The photo resist
layer 290 has been patterned to expose an opening at 295, leaving
separated resist portions shown by way of arrows in the opening.
The photo resist patterning defines areas of the silicon layer 210
in the SOI wafer to be exposed to LOCOS oxidation, for galvanically
isolating circuits therein.
[0040] The width of the opening at 295, and corresponding structure
of the separate portions of the photo resist layer 290, are set to
achieve desired galvanic isolation. This may, for example, involve
setting the width of the opening 295 to correspond with a
particular operating voltage of one or more circuits to be
galvanically isolated, such as described elsewhere in this
document. In some implementations, the width of the opening 295 is
determined using the same criterion as used to set the thickness of
the buried oxide 220 (t.sub.BOX) as discussed above, which may also
be set according to an expected application and desired galvanic
isolation.
[0041] FIG. 4 shows an optocoupler 400 at another stage of
manufacture, according to another example embodiment of the present
invention. A portion of a hard mask layer 280 has been removed at
285, to expose a portion of silicon layer 210. In some
implementations, the portion of the hard mask layer 280 is removed
by dry etching areas to be oxidized using a photoresist 290
patterned as shown in FIG. 3. The dry etch is selective, such that
the etch stops at the silicon layer 210 of the SOI wafer.
[0042] FIG. 5 shows an optocoupler 500 at another stage of
manufacture, according to another example embodiment of the present
invention. As may be implemented relative to FIG. 4, a thermal
oxide 260 is locally grown using a LOCOS process in silicon layer
210 of a SOI wafer, to merge with an underlying buried oxide 220. A
hard mask, such as mask 280 in FIG. 4, can be used to limit the
oxidation of the LOCOS process and set the length L.sub.LI of the
thermal oxide 260. The optocoupler 500 is shown with any such hard
mask having been removed, leaving behind the SOI wafer with
galvanically-isolated regions of silicon layer 210.
[0043] One or both of the length L.sub.LI and thickness T.sub.LI
can be set in accordance with the aforementioned oxide thickness
versus breakdown voltage criterion. In some implementations,
back-end-of-line dielectric isolation is used after the LOCOS
process to reach a desired thickness. In other implementations,
shallow trench isolation is used to provide lateral isolation.
[0044] FIG. 6 shows a top view of an optocoupler device 600,
according to another example embodiment of the present invention.
The device includes transmitter (Tx) portion 610 and receiver (Rx)
portion 620, which are each enclosed in an isolation material 660
such as LOCOS isolation described above. The transmitter portion
610 includes a light-emitting diode 640, and the receiver 620
includes a photodetector 650 that is separated from the
light-emitting diode by the isolation material. The LED 640 and
photodetector 650 are respectively coupled to other circuits in the
transmitter and receiver portions 610 and 620 that operate at
disparate voltages.
[0045] The isolation material 660 is configured with an underlying
insulator to galvanically isolate the transmitter portion 610 and
receiver portion 620 from one another, to facilitate operation of
circuits in each portion at the aforesaid disparate voltages. While
shown surrounding the respective transmitter 610 and receiver 620,
the isolation material 660 can be formed in other manners. For
example, the isolation material 660 can be limited to portions of
the device 600 that are between the transmitter and receiver
610/620 portions, in applications for which these portions are
otherwise galvanically isolated (e.g., via the edge of a chip, or
trench isolation regions).
[0046] FIG. 7 shows a top view of another optocoupler device 700,
according to another example embodiment of the present invention.
The device 700 includes transmitter (Tx) 710 and receiver (Rx) 720
portions, galvanically isolated from one another by an isolation
material 760 and an underlying insulator (e.g., in a SOI structure
as discussed above). The transmitter 710 includes a light-emitter
740, and the receiver 720 includes a light detector 750, such as
described above.
[0047] The emitter/detector pair 740/750 facilitate optical
communications between electric circuits within galvanically
isolated portions of the device 700, with the optical
communications being passed between the emitter/detector to
facilitate communication between the electrical circuits therein.
For example, low-voltage control circuitry in the transmitter
portion 710 can be used to control the operation of high-voltage
circuitry in the receiver portion 720, via optical communication
between the emitter/detector pair 740/750.
[0048] Various embodiments are directed to the integration of
optocoupler circuits such as described herein and/or shown in the
figures, in connection with one or more of a variety of systems.
For example, some embodiments are directed to implementation of an
optocoupler with lighting systems. Control logic and high voltage
drive circuits can be integrated into a single integrated circuit,
facilitating the integration of low-power applications with
high-voltage power switching transistors integrated on-chip. This
approach can be used, for example, in single-chip compact
fluorescent lamp (CFL) controllers. For example, this approach can
be used for driver circuits and power switching transistors used in
110-volt single-chip full-bridge CFL or High Intensity Discharge
(HID) lamp drivers. Other lighting applications include high
frequency tube lighting (HFTL), low-voltage halogen, and LCD
backlighting systems.
[0049] In other embodiments, an optocoupler as discussed herein is
used in smart charger devices that directly handle rectified AC
line supply voltages, for battery charging and power management for
a variety of products. For example, cordless shavers, cellular
telephones, cordless telephones, and other hand-held devices can be
powered using a single-chip system-on-silicon solution circuit as
discussed herein. Power conversion is controlled in response to the
battery condition and load current demand, while at the same time
predicting battery life until the next charge.
[0050] Other embodiments are directed to power supply devices and
systems such as a switchmode power supply (SMPS) systems employing
an optocoupler as discussed herein. High-voltage control circuits
are integrated into a chip also housing high-voltage circuits, with
the control circuits operating at a relatively low voltage. For
certain applications, high-voltage drivers and switching
transistors are combined with analog and digital control circuitry
on a single chip for active power factor correction with power
supplies.
[0051] Flat-screen displays such as those used for monitors and
televisions include an optocoupler circuit as discussed herein, in
connection with other example embodiments. High voltage driver
circuits are integrated with lower-voltage control circuits in a
common chip, with the lower voltage circuits electrically isolated
from the high voltage circuits.
[0052] Based upon the above discussion and illustrations, those
skilled in the art will readily recognize that various
modifications and changes may be made to the present invention
without strictly following the exemplary embodiments and
applications illustrated and described herein. For example,
different types of insulated substrates, different circuit/chip
arrangements, or different positioning of transmitters and
receivers (e.g., as exemplified in FIGS. 6 and 7). Such
modifications do not depart from the true spirit and scope of the
present invention, including that set forth in the following
claims.
* * * * *