Bilithic composite for optoelectronic integration

Optoelectronic composite consisting of two chips, the first chip 10 being made of a first material, the second one 13 being made of another material. The first chip 10, for example, comprises a multiplicity of active optoelectronic devices e.g. a laser diode 11 and a photo diode 12, all being monolithically integrated. A multiplicity of other optical devices, e.g. a waveguide 16, is monolithically integrated on the second chip 13. In addition this second chip 13 has depressions of the size of the devices 11,12 integrated on said first chip 10. These devices and the waveguide 16 of the second chip 13 are automatically aligned when flipping both chips together.

TECHNICAL FIELD 
Disclosed are structures for passive alignment of optoelectronic components 
made in one materials system with other components made in one or more 
dissimilar materials systems. 
BACKGROUND OF THE INVENTION 
Similar to the increasing packaging density in the field of conventional 
semiconductor devices, which started from single elementary devices, as 
e.g. diodes and transistors, and has now reached a point where thousands 
of very small components are three-dimensionally integrated on one chip, 
the integration of optoelectronic components becomes more and more 
important. The trend in optoelectronics is towards integration of active 
optoelectronic devices, passive optical waveguide devices, and functional 
optical waveguide devices to form complete optoelectronic units such as 
for example optical heads for optical disks, optical multi/demultiplexers, 
and circuits for optical computers. Through the optoelectronic 
integration, a more compact, stable, and functional optical system can be 
achieved. 
OptoElectronic Integrated Circuits (OEICs), also known as Optical 
Integrated Circuits (OICs), are divided into two main types from the 
standpoint of materials. When all components of the circuit are integrated 
on a single substrate, such as Si, GaAs or InP, the type of integration is 
called monolithic optoelectronic integrated circuit. A typical monolithic 
optoelectronic integrated circuit with GaAs laser diode 7 and photodiode 
8, integrated on a GaAs substrate 5 with planar waveguide 6, is shown in 
FIG. 1 a). Typical monolithically integrated lasers and other components 
are described in the article "Integrated Optics Approach for Advanced 
Semiconductor Lasers", of Y. Suematsu et al., Proceedings of the IEEE, 
Vol. 75, No. 11, November 1987, pp. 1472-1487. Other examples for the 
monolithic integration of GaAs components on a Si substrate are given in 
the U.S. Pat. Nos. 4,890,895, and 4,774,205. 
When the components are made of different materials and then bonded 
together, this is called a hybrid optoelectronic integrated circuit. For 
example, in a hybrid optical IC, as illustrated in FIG. 1 b), laser diode 
3 is made of aluminum gallium arsenide (AlGaAs), the detector-diode 4 of 
silicon (Si), and the planar waveguide 2, grown on substrate 1, of lithium 
niobate (LiNbO.sub.3). 
Although the monolithic-type OEIC is ideal as an OEIC, implementation is 
very difficult at present. While the performance of monolithically 
integrated GaAs components on Si substrates, see U.S. Pat. No. 4,890,895, 
is good, these components have not yet reached the quality of those 
fabricated using GaAs substrates. Since typical OEICs consist of a number 
of different optical components no one substrate material will be optimum 
for all of them. Thus, a compromise must be made. 
The hybrid type, on the other hand, is relatively easy to fabricate, but 
there is a problem with assembling the basic components. Packaging and 
alignment of these components is time consuming and expensive. 
Nevertheless, the hybrid optoelectronic ICs have the great advantage in 
that what are currently the most appropriate materials and processing 
techniques for each device can be utilized. Because of these advantages, 
hybrid integrated optoelectronic circuits will be subject of intensive 
research and development. 
Different hybrid optoelectronic packages are known in the art, where one or 
more optical fiber(s) is/are connected to an optoelectronic component or 
waveguide. A silicon chip coupling concept is reported on in the article 
"Permanent Attachment of Single-Mode Fiber Arrays to Waveguides", of E. J. 
Murphy et al., IEEE Journal of Lightwave Technology, Vol. LT-3, No. 4, 
August 1985, pp. 795-798. The coupling concept, described by E. J. Murphy, 
is based on a silicon chip having V-grooves for mounting a bundle of 
parallel single-mode fibers. The polished end facets of these fibers are 
butt-coupled to a substrate with waveguides, using optical cement. H. 
Kaufmann et al. describe in their article "Self-Adjusted Permanent 
Attachment of Fibers to GaAs Waveguide Components", published June 1986 in 
Electronics Letters, Vol. 22, No. 12, pp. 642-644, an alignment scheme for 
aligning optical fibers to a GaAs chip. This alignment scheme, called 
V-groove flip-chip mounting technique, is characterized in that two fibers 
and the GaAs chip are mounted on a substrate with V-groove, the alignment 
being achieved by moving the fibers towards the chip along this V-groove. 
Another principle for the alignment of waveguides and/or fibers to 
optoelectronic components is reported on in the U.S. Pat. No. 4,892,374. 
As therein described, an optoelectronic component, e.g. a light emitting 
diode (LED), is bonded in a recessed part of a substrate such that its 
light emitting facet is coupled to a waveguide being integrated on this 
substrate. In the article "Multi-Waveguide/Laser Coupling", of E. B. Flint 
et al., IBM Technical Disclosure Bulletin, Vol. 31, No. 10, March 1989, 
pp. 384-386, a hybrid package is disclosed comprising fibers carried by a 
silicon alignment fixture. For lateral and axial alignments, grooves are 
formed in the top surface of the laser array which has to be coupled to 
the array of fibers, and in the alignment fixture. This package allows 
self-alignment of an array of lasers to an array of fibers. Another 
passive alignment scheme is described in the publication "Passive Coupling 
of InGaAsP/InP Laser Array and Singlemode Fibers using Silicon 
Waferboard", of C. A. Armiento et al., Electronics Letters, Vol. 27, No. 
12, June 1991, pp. 1109-1111. A laser array is aligned to an array of 
fibers by providing for an integration platform with alignment pedestals 
and standoffs on a substrate with V-grooves in which the fibers are 
situated. 
Some disadvantages of the different hybrid alignment schemes cited above 
are their cost and time intensive manufacturing and the non-efficient 
coupling. Another disadvantage is the difficult handling of the small 
components like lasers and other diodes which have to be precisely bonded 
to the substrate. The alignment problems are not known in the area of 
monolithically integrated circuits because the active-, passive-, and 
functional waveguide-devices are automatically aligned by using special 
photolithographic masks, with the drawback on the other hand, that all 
different components have to be made out of the same material. 
These known approaches do not allow for an efficient integration of 
multiple components, waveguides and fibers. No prior art is known, 
relating to simultaneous and self-adjusting alignment schemes for hybrid 
integration of multiple active optoelectronic devices, functional optical 
waveguide devices, and passive optical waveguide devices. 
SUMMARY OF THE INVENTION 
The object of this invention is to provide a method for hybrid integration 
of optoelectronic components such as active optoelectronic devices, 
passive optical waveguide devices, and functional optical waveguide 
devices. 
Another object of this invention is to provide a structure for hybrid 
integration of optoelectronic components such as active optoelectronic 
devices, passive optical waveguide devices, and functional optical 
waveguide devices. 
A further object of the present invention is to improve the performance and 
reliability of optoelectronic integrated circuits OEICs, by making the 
respective components using materials systems which are well suited. 
Another object of the present invention is to provide an alignment scheme 
which allows for automatic alignment of multiple components at the same 
time thus leading to complex and very reliable highly integrated circuits. 
Another object is to improve the overall yield of a complex opto-electronic 
system by making the different types of devices on separate substrates and 
bonding together only those good ones from each type. 
The invention as described and claimed is intended to meet these objectives 
and to remedy the remaining deficiencies of known monolithic and hybrid 
optoelectronic integrated circuits. The principle by which this is 
accomplished is to provide for a bilithic composite having a first 
substrate with components made of a first material, and a second substrate 
with components made of another material, the components being located on 
these substrates such that they are automatically aligned when flipping 
both substrates together.

GENERAL DESCRIPTION 
The next sections relate to different electronic and optoelectronic 
components, some of them requiring special materials, which can be 
integrated in the inventive bilithic composites. The invention allows for 
an integration of conventional electronic components, such as transistors, 
diodes, capacitors, resistances etc., as well as active optoelectronic, 
passive optical waveguide, and functional optical waveguide devices. The 
conventional components are not described in detail because their design 
and fabrication is known in the art. These components can typically be 
fabricated on Si, GaAs as well as other III-V semiconductors, and II-VI 
semiconductors. 
The optoelectronic components are to be divided into three main groups; 
passive optical waveguide devices, active optoelectronic devices, and 
functional optical waveguide devices. Some of these components are listed 
in Tables 1-3. 
Typical passive optical waveguide devices, which exhibit static 
characteristics for optical waves, i.e. those without an optical wave 
control function by external signal, are optical path bending components, 
optical beam dividers, polarizers, wavelength demultiplexers, lenses, 
mirrors, and so forth. Passive materials, incapable of light generation, 
like quartz (SiO.sub.2), lithium niobate (LiNbO.sub.3), potassium niobate 
(KNbO.sub.3), lithium tantalate (LiTaO.sub.3), barium titanate 
(BaTiO.sub.3), arsenic sulphide (As.sub.2 S.sub.3), arsenic selenide 
(As.sub.2 Se.sub.3), tantalum pentoxide (Ta.sub.2 O.sub.5), niobium 
pentoxide (Nb.sub.2 O.sub.5), titanium niobate (TiNbO.sub.3), silicon 
(Si), zinc sulphide (ZnS), calcite (CaCO.sub.3), epoxy, polymide, and 
glass are used for the fabrication of these passive optical waveguide 
devices. The class of passive optical waveguide devices is subdivided into 
bulk components and waveguide components. Examples for bulk components are 
mirrors, lenses, and prisms. Novel functions, not feasible with these bulk 
components, may be obtained by the use of waveguide components. The 
different materials on which these components can be realized are given in 
Table 1. 
TABLE 1 
______________________________________ 
Passive Optical Waveguide Devices 
Component Material/Class of Materials 
______________________________________ 
Prism SiO.sub.2, LiNbO.sub.3, glass, ZnS, Epoxy 
Geodesic Component 
ZnS, Epoxy 
Facet mirror Si, glass, TiNbO.sub.3, ZnS, Epoxy 
Ridge Si 
Reflection type grating 
As.sub.2 S.sub.3, LiNbO.sub.3 
Bent waveguide SiO.sub.2, LiNbO.sub.3, glass, ZnS, Epoxy 
Power divider SiO.sub.2, LiNbO.sub.3, glass, ZnS, Epoxy 
Polarizer LiNbO.sub.3, CaCO.sub.3, Nb.sub.2 O.sub.5 
Wavelength Multiplexer/ 
As.sub.2 S.sub.3, Ta.sub.2 O.sub.5 
Demultiplexer 
Waveguide lens LiNbO.sub.3, As.sub.2 S.sub.3, Ta.sub.2 O.sub.5, ZnS, 
Nb.sub.2 O.sub.5 
Focusing grating coupler 
glass, LiNbO.sub.3 
______________________________________ 
These passive optical devices are described in greater detail in the book 
"Optical Integrated Circuits", of H. Nishihara et al., McGraw-Hill Optical 
And Electrooptical Engineering Series, McGraw-Hill Book Company, 1987, 
Chapter 9. 
Typical functional optical waveguide devices are listed in Table 2. To 
date, a variety of these devices have been proposed and fabricated. In all 
of them the light is essentially controlled via physical phenomena. These 
phenomena are based on ElectroOptic (EO), AcoustoOptic (AO), MagnetoOptic 
(MO), Nonlinear-Optic (NO), and ThermoOptic (TO) effects. Electrooptic 
waveguide devices which employ the electrooptic effect are well known in 
the art, most of them being realized using LiNbO.sub.3 substrates with Ti 
diffused waveguides. Some examples are given in Table 2. 
Acoustooptic devices, based on the acoustooptic effect, provide an 
important means of optical wave control and implements various functional 
devices. The AO devices are classified by their coupling configuration in 
collinear and coplanar devices. They can be further classified by their 
material combination. Exemplary combinations are: 
piezoelectric waveguide and substrate with Ti:LiNbO.sub.3 transducer; 
non-piezoelectric film waveguide (e.g. As.sub.2 S.sub.3) on piezoelectric 
substrate (e.g. LiNbO.sub.3 with LiNbO.sub.3 transducer; 
piezoelectric film waveguide (e.g. ZnO) on non-piezoelectric substrate 
(e.g. SiO.sub.2) with ZnO transducer; 
non-piezoelectric substrate (e.g. SiO.sub.2 /Si) and non-piezoelectric 
waveguide (e.g. As.sub.2 S.sub.3) with thin piezoelectric ZnO transducer. 
Some exemplary AO devices are listed in Table 2. Typical Thin-Film AO 
devices are reported on in the article "Thin-Film Acoustooptic Devices", 
of E. G. H. Lean et al., Proceedings of the IEEE, Vol. 64, No. 5, May 
1976, pp. 779-787. The properties of materials used for Acoustooptic AO 
and Electrooptic EO devices are listed in Table 1 on page 785 of the above 
cited article written by E. G. H. Lean. 
Waveguide magnetooptic devices are implemented by using a waveguide of YIG 
(Y.sub.3 Fe.sub.5 O.sub.12), which is a magnetic material that is 
transparent in the near infrared region. The large Faraday effect, induced 
in this material with a magnetic field that is produced by a small 
current, allows relatively fast optical modulation and switching with low 
driving power, thus being very important for future hybrid OEICs. Examples 
of waveguide MO devices are given in Table 2. 
The effect of non-linearity is used in nonlinear optical devices. These 
devices are also called optical bistable devices. Examples are given in 
Table 2. 
Functional optical waveguide devices employing the thermooptic effect, are 
based on the fact that the refractive index varies with the temperature. A 
stable thermooptic effect is obtained only in the materials without 
deformation or any change in quality caused by a temperature increase. In 
other words, a requirement for the TO waveguide device is that the 
temperature for the waveguide formation is much higher than the operating 
temperature of the device. There are many waveguide materials that meet 
this requirement. Glass waveguides in particular are the most interesting 
of the TO devices. This is why the thermooptic effect can provide the 
functions of light modulation and switching in glass waveguides, which 
have been used to date for passive optical waveguide devices only. 
Examples of TO waveguide devices are given in Table 2. 
TABLE 2 
______________________________________ 
Functional Optical Waveguide Devices 
Material/Class of 
Basic 
Component Material Phenomenon 
______________________________________ 
Phase modulator 
LiNbO.sub.3 EO 
Polarization LiNbO.sub.3, GaAs, InP 
EO 
modulator 
Interferometric 
LiNbO.sub.3 EO 
waveguide modulator 
Optical wavelength 
LiNbO.sub.3 EO 
filter 
Optical switch 
LiNbO.sub.3, LiTaO.sub.3, InP 
EO 
Bragg grating 
LiNbO.sub.3 EO 
Mode converter 
LiNbO.sub.3, glass, ZnO 
AO 
Tunable wavelength 
LiNbO.sub.3, ZnO AO 
filter 
Bragg modulator 
Ta.sub.2 O.sub.5, As.sub.2 S.sub.3, LiNbO.sub.3 
AO 
Bragg deflector 
LiNbO.sub.3 AO 
Mode-conversion type 
YIG (Y.sub.3 Fe.sub.5 I.sub.12), 
MO 
switch GGG (Gd.sub.3 Ga.sub.5 O.sub.12) 
Mode conversion type 
YIG, GGG MO 
modulator 
Optical isolator 
YIG, GGG, LiNbO.sub.3 
MO 
Fabry-Perot resonator 
KTP NO 
2nd harmonic LiNbO.sub.3, Polymers, Knbo.sub.3 
NO 
generation 
Bistable optical 
ZnS, ZnSe NO 
switch 
Cut-off switch 
glass TO 
Branching waveguide 
glass TO 
switch 
______________________________________ 
Typical functional optical waveguide devices are described in the already 
cited book of H. Nishihara. The nonlinear Fabry-Perot Resonator is 
reported on in the special issue of Journal of Quantum Electronics on 
Optical Bistability, edited by E. Garmire, October 1985. In another 
article, titled "Optical Bistability without Optical Feedback and 
Absorption-Related Nonlinearities", the same author describes means for 
obtaining optical bistability employing ZnSe waveguides. This article is 
published in the book "Laser Optics of Condensed Matter", edited by J. L. 
Birman et al., Plenum Press, New York and London, pp. 481-490. Another 
article relating to nonlinear optics (NO), in particular LiNbO.sub.3 
thin-film optical waveguides applications to 2 nd harmonic generation, has 
been published in Journal of Applied Physics, Vol. 70, No. 5, September 
1991, pp. 2536-2541 by H. Tamada et al. The title of this article is; 
"LiNbO.sub.3 Thin-Film Optical Waveguide Grown by Liquid Phase Epitaxy and 
its Application to Second-Harmonic Generation". 
Some examples for active electrooptical devices are; laser diodes, 
photodiodes, light emitting diodes (LEDs), solar cells and so forth. The 
great flexibility of the present invention can be seen by integrating the 
new developed microlasers, which emit light perpendicular to the surface 
of the wafer, instead of conventional diode lasers. These microlasers are 
reported on in the article "Microlasers", J. L. Jewell et al., Scientific 
American, November 1991, pp. 56-62. 
The active electrooptical devices are fabricated on active materials which 
are capable of light generation, such as gallium arsenide (GaAs), gallium 
aluminum arsenide (GaAlAs), gallium arsenide phosphide (GaAsP), gallium 
indium arsenide (GaInAs) and other III-V and II-VI direct bandgap 
semiconductors. The disadvantage of these materials is that they are not 
optimum for the integration of the passive optical and functional optical 
waveguide devices. Typical active electrooptical devices are listed in 
following Table 3. 
TABLE 3 
______________________________________ 
Active Electrooptical Devices 
Component Material/Class of Materials 
______________________________________ 
Laser diode GaAs, InP, III-V, II-VI semiconductors 
Microlaser diode 
GaAs 
Light emitting diode 
GaAs, InP, III-V, II-VI semiconductors 
PIN photodetector 
GaAlAs, III-V semiconductors 
______________________________________ 
Embodiments of the present invention comprising some of the above listed 
active electrooptical, passive optical waveguide, and functional optical 
waveguide devices are described in connection with FIGS. 2-12. The 
principle of the present invention is described in context with the first 
embodiment, illustrated in FIGS. 2 and 3. This embodiment consists of two 
chips 10 and 13, the upper one being made of a first material, e.g. an 
active material like GaAs, and the second one being made of a second 
material, e.g. a passive material like LiNbO.sub.3. Two active 
electrooptical devices, a laser diode 11 and a photodiode 12 are 
fabricated on this first chip 10. The second chip 13 comprises a passive 
optical device, a Y-shaped waveguide 16 being made by Ti diffusion in 
LiNbO.sub.3 substrate, and two depressions 14, 15 which have the size of 
the components 11 and 12 on the first chip 10. The positions of the 
depressions 14 and 15 on chip 13 and the alignment of the depressions 14 
and 15 with respect to the waveguide 16 are defined by the lithographic 
masks used during the fabrication of this chip. As shown in FIG. 3, both 
chips 10 and 13 form a composite when urged together such that all 
components of the respective chips are automatically aligned. In the first 
embodiment the two active devices 11 and 12, and the depressions 14 and 15 
on the facing side serve as mechanical alignment means bringing both chips 
into an optimum position. The composite, consisting of two chips joined 
together, may be mounted on a mounting base in a metal housing and a 
conventional piston or spring may provide for thermal heat transfer 
between the heat sources on the chips and a heat sink. 
Features of the present invention are: 
The accurate permanent passive alignment of the components of one chip 
relative to the other components; 
The simultaneous alignment of many optical and, as shown in another 
embodiment, electronic components with one alignment step; 
The ability to fabricate transparent waveguides, functional optical 
waveguide devices and passive optical devices on the `passive` chip which 
have low losses and optimum quality for the respective components (not 
achievable by monolithic integration); 
Since the `active` and `passive` chips can be fabricated separately the 
yields of the bilithic composite are not the product of the yields of each 
chip. Good samples of each `active` and `passive` chip can be selected by 
testing them prior to joining them together; 
Substrates can be chosen which optimize fabrication of the active 
electrooptical devices, passive optical waveguide devices, and functional 
optical waveguide devices separately, e.g. a LiNbO.sub.3 chip could be 
combined with a GaAs chip for matching of nonlinear optical (NO) devices 
with lasers; 
The active electrooptic devices, passive optical waveguide devices, and 
functional optical waveguide devices can be made in any number, and any 
orientation using etched mirror technology on their respective substrates; 
Conventional electronic components as transistors, diodes, capacitors, 
resistances, driver circuits and so forth can be integrated on one of the 
chips forming a complete functional unit; 
Complete and complex circuits can be made using only two different 
substrates and one alignment step during packaging; 
Vertical alignment as well as horizontal alignment is defined by 
microlithographic techniques and is thus very accurate; 
Each chip can carry means for electrical and/or optical interconnections, 
such that for example wires can be coupled, e.g. by aligning them in 
V-shaped grooves, to the waveguides on the respective chip. 
The chips are limited in size only by differential thermal expansion of the 
composite. The layout of the chips and the design of the alignment means 
have to be made such that thermal heating, caused by heat sources on the 
chips, does not lead to stress or strain capable of destroying the 
composite or even reducing the coupling efficiency between the components. 
The maximum allowable temperature raise can be estimated using the 
following equation: 
##EQU1## 
wherein T.sub.CE are the temperature coefficients of the substrates 1 and 
2, 1 is the length of the overlap between the chips, and .DELTA.1 is the 
maximum alignment tolerance. For instance in a composite of a Si chip 
(T.sub.CE.sbsb.1 =2.6.times.10.sup.-6) and a GaAs chip (T.sub.CE.sbsb.1 
=6.86.times.10.sup.-6), both chips being square chips with a length of 
1=0.01 m, and with a maximum alignment tolerance of 0.1 .mu.m (which is 
quite aggressive), the allowable .DELTA.T is about 2.degree. C. This 
.DELTA.T is quite simple to achieve with conventional Peltier coolers for 
example. A list of temperature coefficients is given in Table 4. More 
details about these materials can be taken from standard reference works. 
TABLE 4 
______________________________________ 
Temperature Coefficients of Thermal Expansion 
Material T.sub.CE [.degree.C..sup.-1 ] 
______________________________________ 
GaAs 6.86 .times. 10.sup.-6 
Si 2.6 .times. 10.sup.-6 
SiO.sub.2 0.5 .times. 10.sup.-6 
InP 4.75 .times. 10.sup.-6 
LiNbO.sub.3 4 .times. 10.sup.-6 
CaCo.sub.3 21 .times. 10.sup.-6 
ZnO 6 .times. 10.sup.-6 
GaP 4.65 .times. 10.sup.-6 
BaTiO.sub.3 1.9 .times. 10.sup.-5 
As.sub.2 S.sub.3 
2.4 .times. 10.sup.-5 
ZnS 6.9 .times. 10.sup.-6 
glass see literature (.about.3 .times. 10.sup.-6) 
______________________________________ 
With the employment of different alignment means it is possible to achieve 
vertical and horizontal alignment as well as mechanical alignment of the 
chips comprising the inventive composites. Some exemplary alignment means 
are illustrated in FIG. 4. An electro-plated pillar 42 of any convenient 
material such as grown on top of a plating base 43 by conventional 
techniques, and a depression 41.1 on the opposite side, see FIG. 4 a), can 
be employed to align upper chip 40 relative to lower chip 41. 
Electro-plated pillars and similar means are well suited because of the 
high aspect ratio (aspect ratio: height/width) that can be achieved. Chip 
44, shown in FIG. 4 b), has a ridge 47 made of the same material as the 
substrate. A depression 46 in the opposite chip 45 is designed such that 
the ridge 47 fits into this depression when fitting chips 44 and 45 
together. The side walls of this ridge are dry-etched such that they are 
perpendicular to the chip's surfaces. Similar alignment means for the 
alignment of chips 48 and 49, are illustrated in FIG. 4 c), with the only 
difference that the side walls of ridge 51 and depression 50 are 
wet-etched, giving a slanting side wall. The example shown in part d) of 
FIG. 4 serves as fiber holder and in addition aligns the upper chip 52 and 
lower chip 53 at the same time. To achieve this, fiber 54 is situated in 
V-shaped grooves of the chips 52 and 53. 
The cross-sections of possible alignment means are illustrated in FIG. 4, 
not showing where to place these means on a chip. An example is 
illustrated in FIG. 5. Shown is the top view of a chip 55 which has two 
depressions 56 and 57. The depression 56 has a rectangular shape and the 
depression 57 a rectangular shape. The upper chip which has to be flipped 
onto the lower chip 55 is not shown in this Figure. Only alignment means 
58.1-58.3, with circular cross-sections are schematically illustrated. 
These alignment means 58.1-58.3, e.g. metal balls or cylindrical pillars, 
fit into the depressions 56 and 57 of chip 55. Alignment means 58.2 
defines the position of the upper chip relative to the lower one, but does 
allow rotational movements around an axis parallel to the z-axis. 
Alignment means 58.1 allows linear movements parallel to the y-axis, for 
example linear movements caused by temperature differences in the 
composite, but prevents rotational movements around an axis parallel to 
the z-axis. Pillar or ball 58.3, which is not guided by a depression on 
chip 55, is the third standpoint allowing rotational as well as linear 
movements in the x-y plane. Different combinations of these and other 
alignment means are conceivable. In addition to these alignment means, the 
components on one chip can be placed in depressions of the opposite chip, 
to align both chips of a composite, as illustrated in FIG. 3. 
The second embodiment of the present invention is described below with 
reference to FIG. 6, showing the upper chip 60 and the lower chip 64. FIG. 
7 shows two magnified perspective sketches of portions of chip 64 
indicated by circles labelled 7a and 7b. The upper chip 60 consists of InP 
and comprises four InP/InGaAsP laser diodes 62.1-62.4 with etched mirrors 
and a bidirectional 4.times.4 optical InP switch 61. This optical 
4.times.4 switch is an electrooptical functional waveguide device which 
achieves switching action through carrier injection thus causing a change 
in the refractive index. More details of this respective switch, which may 
be replaced by other types of switches, is reported on in the publication 
"NCM, Network Configuration Module, Optical Switch", issued by Siemens AG, 
Gesch&ae.ftsgebiet &Oe.ffentliche Vermittlungssysteme, Postfach 70 00 73, 
8000 Munich 70, Germany, Order No.: A30930-N1250-P24-1-7629. Bonding pads 
63 are situated on the left hand side of chip 60. These pads are connected 
with the active devices 61 and 62.1-62.4 and provide for electrical 
interconnection ports to other circuits, power supply etc. The bonding 
pads 63 and the respective conducting paths are only schematically shown. 
The lower chip 64 is designed such that the upper chip 60 overlaps the left 
portion of it when flipping them together. Chip 64 consists of 
LiNbO.sub.3. On the opposite side of the laser diodes 62.1-62.4 and the 
optical switch 61, are depressions 66.1-66.4, and 65 situated, having the 
size of these active devices. Chip 64 further comprises waveguides, 
waveguide directional couplers 68.1-68.4, V-shaped grooves 70.1, and 
optical isolators 67.1-67.4. The V-shaped grooves serve as alignment means 
for external optical fibers which have to be coupled to the composite. A 
V-shaped groove 72 with optical fiber 69.1 is schematically shown in FIG. 
7 a) in form of a magnified perspective sketch. As can be seen from this 
Figure, a V-shaped groove 72 is etched into the LiNbO.sub.3 substrate 64 
such that the end facet of this groove is aligned to the Ti diffused 
LiNbO.sub.3 waveguide 73. Details of materials and fabrication techniques 
of optical waveguides, in particular Ti:LiNbO.sub.3 waveguides, are given 
in chapter 6 of the book "Optical Integrated Circuits" , of H. Nishihara 
et al., McGraw-Hill Optical And Electrooptical Engineering Series, 
McGraw-Hill Book Company. Another fabrication technique of LiNbO.sub.3 
waveguides is reported on in the article "Laser Micro-Fabrication of 
Waveguide Devices", B. Fan et al., IBM Technical Disclosure Bulletin, Vol. 
31, No. 11, April 1989, pp. 150-152. 
The external fiber 69.1 is fixed in groove 72 by moving it towards the 
waveguide 73 and fixing it in the optimum position with an optical cement. 
These fiber to waveguide couplers are known in the art and their coupling 
efficiency is quite good. Two papers reporting on this coupling principle 
are; "Passive Coupling of InGaAsP/InP Laser Array and Singlemode Fibers 
Using Silicon Waferboard", C. A. Armiento et al., Electronics Letters, 
Vol. 27, No. 12, June 1991, pp. 1109-1111, and "Self-Aligned Flat-Pack 
Fiber-Photodiode Coupling", B. Hillerich, A. Geyer, Electronics Letters, 
Vol. 24, No. 15, pp. 918-919. 
A magnified perspective sketch of waveguide directional coupler 68.4 is 
illustrated in FIG. 7 b). The principle of these waveguide directional 
couplers 68.1-68.4, which are integrated on chip 64, is described in the 
book "Optical Integrated Circuits", of H. Nishihara et al., McGraw-Hill 
Optical And Electrooptical Engineering Series, McGraw-Hill Book Company, 
Chapter 9. The separation g between the upper waveguide, with reference 
number 76.1, and waveguide 75 should be about 2 .mu.m. A lightwave emitted 
by laser diode 62.4 travels through waveguide branch 76.1, passes the 
`knee` 77, and leaves the waveguide directional coupler 68.4 at branch 
76.2. A lightwave arriving at the opposite side, at branch 76.2, and 
having the power P.sub.2, is to a great amount coupled into the second 
waveguide 75, where it is fed to fiber 69.4. The power P.sub.2 of this 
lightwave, being coupled into waveguide 75, is smaller than P.sub.1. The 
remaining portion of the lightwave, not being coupled into waveguide 75, 
has the power P.sub.3 =P.sub.1 -P.sub.2. To prevent optical feedback to 
the laser diodes 62.1-62.4, which may cause damage of these diodes, 
optical isolators 67.1-67.4 are inserted between the waveguide directional 
couplers 68.1-68.4 and these diodes. 
The optical isolators, as for example described in chapter 10 of the book 
"Optical Integrated Circuits", of H. Nishihara et al., McGraw-Hill Optical 
And Electrooptical Engineering Series, McGraw-Hill Book Company, are 
comparable to an ideal diode. This optical isolator is able to guide a 
lightwave, which is inserted on the left hand side (present embodiment), 
to the waveguide directional coupler and the following optical 4.times.4 
switch 61 with very low losses. Light arriving from a waveguide coupler at 
this optical isolator is stopped, such that no light arrives at the laser 
diodes. This second embodiment shows some details of how to implement the 
present invention. More exemplary details are given in FIGS. 8-12. 
FIG. 8 shows a cross-section through a composite in accordance with the 
present invention. The upper chip 80, in the following referred to as 
`active` chip, comprises a laser diode 85 with etched mirrors and a metal 
pillar 83 being electro-plated on top of a plating base 82. The method for 
making laser diodes with etched mirrors, as integrated on the `active` 
chip 80, is disclosed in the European Patent Application with publication 
number 0 363 547, "Method for Etching Mirror Facets of III-V Semiconductor 
Structures". 
The opposite chip 81, hereinafter referred to as `passive` chip, comprises 
a schematically shown waveguide 86 and a depression 84. When flipping the 
`active` and `passive` chips together, the metal pillar 83 fits into the 
depression 84 such that the light emitting facet of laser diode 85 is 
aligned to waveguide 86. This waveguide 86 has an inclined facet 87 at its 
end which reflects the laser beam 89 into the substrate of the `passive` 
chip 81. Laser beam 89 is reflected at the backside 88 of this chip and 
leaves the chip pointing upwards. The following articles report on 
waveguides with inclined facet: 
"Fabrication and Application of Beveled Structures in Optical Waveguides", 
M. M. Oprysko et al., IBM Technical Disclosure Bulletin, Vol. 32, No. 11, 
April 1990, pp. 305-307; 
"Beveled Waveguides for Flip Chip Opto-Electronic Receivers", E. B. Flint 
et al., IBM Technical Disclosure Bulletin, Vol. 33, No. 7, December 1990, 
pp. 194-196; 
"Three-Dimensional Optical Waveguide Splitter", M. M. Oprysko et al., IBM 
Technical Disclosure Bulletin, Vol. 34, No. 5, October 1991, pp. 46-48. 
As can be seen from these exemplary articles, different solutions are known 
in the art for the implementation of means which reflect a beam out of a 
waveguide. The materials of both chips 80 and 81 and the components 
integrated on these chips can be chosen as shown in Tables 1-4. 
Another implementation of the present invention is illustrated in FIG. 9. 
Similar to the composite shown in FIG. 8, the `active` chip 90 comprises a 
laser diode 93 with etched mirrors. The `passive` chip 91 comprises a 
depression 92, which has the size of said laser diode 93, and a 
schematically shown waveguide 94 which is aligned to the depression 91. 
When flipping both chips together, as shown in FIG. 9, the laser 93 fits 
into depression 92 and is automatically aligned to waveguide 94. Laser 
beam 95, emitted by laser 93, is guided through this waveguide and coupled 
out of the composite. In this example, the laser diode 93 on one side and 
the depression 92 on the other side serve as alignment means. 
Another illustrative composite, its cross-section being shown in FIG. 10, 
requires a greater distance between `active` and `passive` chips 100 and 
101. Again a laser diode 104 is situated on the `active` chip 100. 
Additionally an electro-plated mirror 105.1, oriented at 45.degree., which 
is electro-plated on plating base 103.2, and a depression 109 are situated 
on chip 100. `Passive` chip 101 comprises a pillar 102 formed on top of a 
plating base 103.1 and a waveguide 108. This waveguide has an inclined 
facet 108.1 at one end to receive a vertical beam from mirror 105.1 and 
direct it horizontally. A waveguide collimating lens 106 and a focusing 
grating coupler 107 are situated on top of waveguide 108. The waveguide 
lens 106 is used to collimate the waveguide mode travelling to the right 
through waveguide 108 and focusing grating coupler 107 focuses the light 
out of waveguide 108 into focus point F. Details of focusing grating 
coupler 107, in combination with collimating lens 106, are given in the 
article "Rotationally Symmetric Construction Optics for a Waveguide 
Focusing Grating" , G. N. Lawrence et al., Vol. 29, No. 15, May 1990, pp. 
2315-2319. 
FIG. 11 shows a packaging example for an inventive composite. This 
composite, comprising an upper chip 114, which is the `passive` one, and a 
lower, `active` chip 113, is mounted on a mounting base 111. The whole 
composite is encapsulated in a metal housing 110 which has a window 118 
serving as optical interconnection port. Two metal pins 112.1 and 112.2 
are schematically shown, providing for an electrical interconnection 
between the composite and other circuits. The composite is connected via 
metal wires, one of them, with reference number 117, being shown in FIG. 
11, to said pins. A piston 116 serves as heat transfer bridge between the 
backside of chip 114 and the housing 110. This heat transfer bridge may be 
replaced by other bridges as described in the European Patent Application 
with application number 91810342.5, "Cooling Structures and Package 
Modules for Semiconductors". Mounting base 111 serves as heat transfer 
bridge between the `active` chip and the housing 110. A mirror 115, in 
particular an electro-plated mirror, is situated on the lower chip 113 
such that a light beam emitted by the upper chip 114 is reflected through 
window 118 out of the housing. Different other packaging modules for 
composites in accordance with the present invention will be readily 
apparent to those skilled in the art. The `passive` chip, for example, may 
be directly mounted on the mounting base and the upper, `active` chip may 
be cooled via a capstan, piston, or a spring. 
FIG. 12 illustrates a detail sketch of an inventive composite. This 
composite comprises a lower chip 121 with an electro-plated metal plate 
122, and another chip 120 with an active component 123. The upper chip 120 
is flipped onto the lower one such that the active component 123 is 
thermally connected, either directly or via a thermal grease, to the metal 
plate 122. This plate serves as a heat sink or a heat transfer bridge. In 
addition this metal plate can be used as electric contact to the active 
component. Similar to the embodiments disclosed in the above cited 
European Patent Application 91810342.5, a metal structure, called cooling 
structure, may be electro-plated on top of the active devices of an 
`active` chip, forming a very efficient heat transfer bridge or a heat 
sink for smaller heat sources. Very efficient cooling of the composite is 
required to prevent damage caused by thermally induced stress or strain 
and to avoid thermal cross-talk between active devices. As mentioned, a 
Peltier element can be employed to control the temperature of the 
inventive composites.