Patent ID: 12219878

DETAILED DESCRIPTION

The optoelectronic component according to the invention comprises an optical transducer made of III-V semiconductor material and an optical scanning microelectromechanical system, denoted MEMS, comprising a mirror. The optical transducer and the optical scanning microelectromechanical system are produced in a common wafer comprising at least a first layer made of silicon or silicon nitride with a thickness of less than one micron and in which at least the mirror and its holding springs are produced.

The first layer of silicon or silicon nitride advantageously has a thickness greater than or equal to 300 nm.

The first layer made of silicon or silicon nitride is in one piece and comprises the mirror and its holding springs.

The wafer comprises the first layer made of silicon or silicon nitride and a second layer made of silicon oxide. An optical guide is contained within these two layers.

The optical guide comprises an optical structure formed in the first layer made of silicon or silicon nitride and the second layer made of silicon oxide, which contributes to the confinement of the optical mode.

Advantageously, the optical guide is formed so as to guide light in the plane of the first layer made of silicon.

Producing the optical guide within one and the same layer as the mirror and its springs makes it possible to obtain a small component and to avoid a step of depositing or growing an additional layer.

It also makes it possible to achieve precise alignment of the mirror with the optical guide and to achieve emission or reception both in a direction perpendicular to the plane of the first layer and in a direction of the plane of the first layer. Indeed, the optical guide makes it possible to guide light in the plane of the layer. The mirror makes it possible to direct light in all directions out of the plane of the layer and into the plane of the layer.

There are notably two possible embodiments of the component. In a first embodiment, the mobile parts of the optical scanning microelectromechanical system are produced in layers of silicon or silicon oxide. In a second embodiment, the mobile parts of the optical scanning microelectromechanical system are produced in the layer of III-V semiconductor material.

The optical transducer may be either a light emitter or a light receiver. In the first case, the emitter is a laser. In the second case, the receiver is a photodiode. In the following text, the term transducer covers its two functions.

As a first exemplary embodiment,FIG.1shows the stack of layers needed to produce a component according to the invention in a first embodiment. This figure and those that follow are referenced in a three-dimensional reference system (O, x, y, z). The cutting plane ofFIG.1is in a plane (O, x, z). Proceeding from outside the component1to the substrate serving as support therefor, the following are found in succession:a layer 2 of III-V material,a thin transfer layer 2bis of silicon oxide of around one hundred nanometers, which makes it possible to transfer the previous layer 2 onto the following layer 3,a first layer 3 made of silicon or silicon nitride, whose thickness E3is of the order of 500 nanometers,a second layer 4 made of silicon oxide, whose thickness E4is between 3 microns and 4 microns,a third layer 5 made of silicon, whose thickness E5is between 10 microns and 100 microns,a fourth layer 6 made of silicon oxide, whose thickness E6is between 3 microns and 4 microns,the actual substrate7, made of silicon.

The transducer is made of III-V material such as indium phosphide or InP into which quantum wells are integrated. This material is then transferred onto the substrate made of silicon. The one or more optical guides is or are manufactured in the first layer 3 made of silicon or silicon nitride.

The mirror30and its holding springs31are produced in the first layer 3 made of silicon or silicon nitride.

The second layer 4 made of silicon oxide, located just under this first layer of silicon or silicon nitride3, contributes to the confinement of the optical mode. In other words, the second layer 4 is contiguous with the first layer 3. The second layer 4 forms a wall of the optical guide.

The much thicker third layer of silicon is used to produce the actuators of the MEMS device for deflecting the emitted or received light beam, depending on whether the transducer is an emitter or a receiver.

In particular, mobile parts23,24,25of the MEMS device are produced in the third layer 5 of silicon. The mobile parts23,24,25are able to actuate, that is to say mechanically drive, the mirror30and its springs31.

The third layer 5, comprising the mobile parts23,24,25, is in one piece.

To produce the component, it is necessary to use special semiconductor wafers, as they are known. These are silicon wafers having two buried layers of silicon oxide. The one or more optical guides is or are thus produced in the upper layer of silicon or silicon nitride, and the mechanical structures are produced in the intermediate layer made of silicon.

One solution for obtaining such wafers is to use a conventional wafer called silicon on insulator, or “SOI” in acronym form, to produce the structures of the MEMS. These wafers are commercially available. This wafer comprises the substrate made of silicon, the layer of silicon oxide with a thickness of a few microns and the upper layer of silicon with a thickness of a few tens of microns, which will be used to produce the MEMS mechanical structure. On this wafer, a new layer of silicon oxide with a thickness of 3 to 4 microns is grown, obtained by oxidizing superficial silicon in a suitable furnace. The guide layer made of silicon or silicon nitride is deposited on this last layer of silicon oxide.

The III-V components are produced in a conventional manner, starting by structuring the optical guides and the functions produced in the upper silicon or silicon nitride, and then transferring the III-V materials and arranging them. These manufacturing steps are performed until complete with the necessary metallizations, taking into account the definition of the optical output facets of the components.

The parts of the wafer comprising the III-V components on silicon or silicon nitride and in particular the output facets of the components are then protected by resin or possibly photoresist.

Finally, the mechanical devices of the MEMS and the mirror are produced. This production comprises the following steps:Cutting the mirror from the upper layer of silicon through photolithography and silicon etching;Producing the MEMS actuators through masking and deep reactive ion etching, known as “DRIE”;Producing the necessary trenches under the mirror through masking and isotropic etching;Metallizing the MEMS structures and the mirror;Releasing the mobile parts and the mirror through hydrofluoric acid or HF etching of the two layers of silicon oxide.

Once the MEMS structures and the mirrors have been produced, the protective resin for the III-V components, deposited before the MEMS manufacturing steps, is removed.

There are various configurations for producing the mirror scanning microelectromechanical system according to the invention. By way of non-limiting example,FIG.2shows a plan view of the component according to the invention comprising its transducer10and its microelectromechanical system20. This view is in a cutting plane (O, x, y).

The microelectromechanical system20comprises two identical actuators and a one-piece assembly produced in the first layer comprising the mirror30and its two holding springs31. This assembly is shown in gray inFIG.2.

Each actuator consists of two fixed combs21and22that are identical and symmetrical to one another and a mobile double comb23comprising a central beam24. The teeth of the mobile comb are interwoven with those of the two fixed combs.

The central beam24is connected to a second beam25, perpendicular to said beam24. The two beams25of the two actuators are parallel to one another. Each of these two beams25is connected to one of the two holding springs31.

The fixed combs and the mobile comb of the actuators are voltage-controlled. The control voltages for the fixed parts are a few tens of volts. By way of example, the control voltages +V and −V inFIG.2are +50 V on the first fixed comb and −50 V on the second fixed comb. The control voltages Va for the mobile comb are a few volts.

The voltage control of an actuator leads to the translational displacement of the mobile comb and, therefore, that of the beam25, which moves in the direction of its length. The displacements are shown by white arrows inFIG.2and those that follow.

Each holding spring31comprises a leaf in the shape of an elongated rectangle connected to the mirror30by a connection of very small width. Given their very small thickness, the leaves have a certain elasticity and may thus buckle easily. InFIG.2, the mirror30is of circular shape.

The operation of the device is shown inFIGS.3,4and5,FIG.5showing an enlarged partial view ofFIG.4. InFIG.5, the square-shaped white arrow shows the deflection of the light beam by the mirror when the transducer is a laser.

FIG.3shows a side view of the mirror30and of its holding springs31in the absence of stresses from the interdigitated combs. This side view is shown in a cutting plane (O, x, z). The mirror and its springs are in a horizontal plane, parallel to the axis x. No deflection takes place.

FIG.4shows a side view of the mirror and of its holding springs in the presence of stresses from the interdigitated combs. Applying the control voltages leads to the displacement of the two springs, as may be seen in thisFIG.4, which come into abutment under the first layer of silicon or silicon nitride arranged under the III-V transducer referenced10.

This abutment guidance is provided by a potential difference applied between the second layer and the thick third layer of silicon. The area of the mirror is thus positioned under the layer of silicon used for optical guidance. If the displacement is continued, the leaves of the springs buckle, causing the mirror to rotate.

If the displacements of the two springs are identical, the mirror rotates about the axis y and straightens, as may be seen inFIGS.4and5. If the displacements of the two mirrors are different, the mirror rotates about the axis z. It is thus possible, simply by adjusting the control voltages, to obtain an orientation of the mirror along two different axes, making it possible to deflect a light beam emitted or received along these two axes. Knowing the relationship that links the control voltages to the orientations of the mirror, it is thus possible to obtain the desired deflection.

As a second exemplary embodiment,FIG.6shows the stack of layers needed to produce a component according to the invention in a second embodiment. The cutting plane ofFIG.6is in a plane (O, x, z). Proceeding from outside the component1bis to the substrate serving as support therefor, the following are found in succession:a layer 2 of III-V material,a thin transfer layer 2bis of silicon oxide of around one hundred nanometers, which makes it possible to transfer the previous layer 2 onto the following layer 3,a first layer 3 made of silicon or silicon nitride, whose thickness is of the order of 500 nanometers,a second layer 4 made of silicon oxide, whose thickness is between 3 microns and 4 microns,the actual substrate7, made of silicon.

As in the previous first embodiment, the transducer is made of III-V material such as indium phosphide or InP into which quantum wells are integrated. This material is then transferred onto the substrate made of silicon. The optical guides are manufactured in the first layer 3 made of silicon or silicon nitride.

The second layer 4 made of silicon oxide, located just under this first layer 3 of silicon or silicon nitride, contributes to the confinement of the optical mode. In other words, the second layer 4 delimits the optical guide.

The essential difference from the first embodiment is that the mechanical device21,22,23,24,25for deflecting the light beam is produced in the III-V layer. A mechanical device for deflecting the light beam is understood to mean the actuators21,22,23,24,25of the MEMS device, that is to say the actuators of the mirror30and of its springs31. The layer of III-V material is in one piece.

This may comprise the same components as the previous deflection device shown inFIG.2. The components are arranged in the same way, but the actuators21,22,23,24,25are produced in the layer of III-V material. They comprise, as in the previous case, a symmetrical structure with interdigitated combs connected by beams to an assembly comprising two leaf springs31supporting a mirror30positioned in front of the transducer.

The operation of the device is indicated inFIGS.7and8, which show a side view of the mirror and its holding springs in the absence and in the presence of stresses from the interdigitated combs. This side view is shown in a cutting plane (O, x, z). As in the previous embodiment, the mirror and its springs are produced in the thin layer of silicon or silicon nitride. The mechanism for orienting the mirror is the same. By applying identical or different control voltages to the actuators, the mirror is oriented along two different axes.

The abutment guidance for the mirror is provided by a potential difference applied between the second layer and the substrate.

One of the benefits of this second embodiment over the previous one is that, since the number of layers required is lower than the first embodiment, the components may be implanted on standard wafers of simpler design, already used to produce III-V components heterogeneously integrated on a standard wafer. If necessary, the substrate made of silicon may be etched and used to produce parts requiring suitable mechanical properties.

Producing this type of component comprises the following steps:Producing the mechanical structures made of III-V materials with three steps of masking, DRIE etching and isotropic etching for the trenches;Producing the mirror and its holding springs by clearing the upper layers up to the layer of silicon or silicon nitride and then by masking, RIE etching and isotropic etching to define the mirror and its retaining springs and prepare their release;Metallizing the MEMS structures in order to make electrical contact and define the mobile mirrors;HF acid etching in order to release the mobile parts of the various devices;Once the structures of the MEMS and the mirrors have been produced, removing the protective resin for the III-V components, deposited before the MEMS manufacturing steps.

In this embodiment, the III-V layer is deposited on the wafer before the stage of producing the mechanical structures.

The component according to the invention may comprise a plurality of transducers and/or multiple MEMS and/or a plurality of optical guides.