Micro opto electro mechanical device

#The present invention relates to Micro Electro Mechanical Systems (MEMS) devices for use in optical systems, especially optical systems for telecommunications. In particular, but not exclusively, the invention relates to MEMS devices for use as variable optical attenuators or optical switches.

#There is a requirement in the telecommunications industry for optical components which function as switches or attenuators for optical networks. Recently, there has been a great deal of interest in optical switches and attenuators based on MicroElectroMechanical Systems (MEMS). WO 98/12589 describes one such switch which is fabricated from a single substrate. Deep Reactive Ion etching (DRIE) is used to form an actuator and a vertical shutter which can be moved by the actuator into or out of a switching region between the ends of one or more optical fibres held in trenches etched in the substrate, so as to switch an optical signal from one optical fibre to the other by reflection off the shutter. The switching region is filled with index-matching fluid to avoid undesirably high losses due to mismatch of refractive indexes in the switching region. The whole switch therefore needs to be sealed from the environment, in order to contain the index-matching fluid within the switch. A disadvantage of this type of device is that there is the possibility of leakage from the package. Moreover, the packaging of such a fluid-filled package is a very complex operation. Also, the long term stability and thus performance of such index-matching fluids is not fully known.

#In order to allow greater potential for integration of active and passive optical components, there is however a desire to move away from fibre-based components, to components made using planar waveguide technology. U.S. Pat. No. 6,195,478B describes an optical switch based on planar waveguide technology. In this switch a shutter formed using MEMS technology can be displaced (by a MEMS actuator) along a trench formed between at least two waveguide ends, to effect switching of an optical signal from one waveguide to another by reflection off the shutter. In one embodiment the trench is filled with index-matching fluid, and so again the whole switch needs to be enclosed in an outer package to contain this fluid therein. In other embodiments, the trenches are filled only with air, but even in these latter embodiments it is necessary to seal the whole switching component hermetically from the surrounding environment, in order to protect the delicate structure of the MEMS components from damage from moisture, small particles or other environmental contaminants. This present significant problems, for example this requires the outer package for the device to be made from specific materials known to provide hermetic sealing, and for complex package sealing operations to be performed by skilled operators in order to meet industry hermetic package requirements. Additionally there is the problem that such a hermetic package restricts the type of materials which can be used inside the package: because nothing can pass into the package or out of the package, therefore nothing can be contained inside the package that would cause harm.

#Preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

#FIG. 1 is a plan view of a packaged optical component according to an embodiment of the invention, in which a lid of the package has been removed to reveal the contents of the package;

#FIG. 2 is a cross-sectional side view, taken along the line A–A′ of FIG. 1, of a portion of the optical component of FIG. 1 comprising a PLC chip with a MEMS chip flip-chip bonded thereto;

#The invention concerns a locally hermetically sealed SOI MEMS device bonded to a PLC substrate such that the MEMS device is able to interact optically with the optical field in the PLC. The device does not require package level hermetic sealing from the environment. The invention also concerns the processing route towards this sealed hybrid device. The claimed invention is not specific to the final functionality of the device, that is the device created could be a VOA, a switch, or some other device where controlled optical interaction between a MEMS device, a waveguide and an optical beam is required. While the specifics of the waveguide pattern and MEMS device details may change to accommodate the different functions, the process flow for fabricating the packaged component will remain substantially unchanged. A VOA device in accordance with one embodiment of the invention will now be described. The extension to a switch application is described as a second embodiment thereafter.

#As will be readily understood in the art, the term “hermetic” is used to refer to devices, materials or structures which form an air-tight seal, usually with an associated maximum allowable leak rate and/or internal moisture content e.g. Telcordia GR-1221 standards define a maximum internal moisture content of 5000 parts per million water vapour (for a hermetic package). Usually, a hermetic seal is formed at an interface between glass and/or metallic surfaces, but there are also other materials potentially capable of providing a hermetic seal such as silicon or ceramic materials.

#FIGS. 1 and 2 show an optical component comprising a VOA device 1, according to one embodiment of the invention. The device comprises a first substrate 2 having a planar lightguide circuit (PLC) formed thereon (hereinafter referred to as the “PLC chip”), and a second substrate 3 having a MEMS device formed thereon (hereinafter referred to as the “MEMS chip”) and which is flip-chip bonded to the PLC chip. The MEMS chip 3 sits in a well 5 provided therefor in the PLC chip 2. A hermetic cap 4 is sealed to the PLC chip so as to house the MEMS chip 3 between the PLC chip 2 and the cap 4. The whole device so assembled is housed within a (non-hermetic) housing 9. A fibre V-groove array (FVA) device 17,19 connects an input fibre I and an output fibre O to input and output edges 2a, 2b respectively of the PLC chip. Two glass rails 2c, 2d (not shown in FIG. 2) are attached to an upper surface of the PLC chip 2, adjacent to the chip's input and output edges 2a, 2b respectively and arranged parallel to these edges, to increase the bonding area available to bond the FVAs to the chip. This bonding area is sometimes referred to as the “bond line”. (In other possible embodiments other ways of connecting the input/output fibres to the PLC chip may be used.) Electrical connections 18a, 18b are provided for carrying operating electrical signals to and from the device inside the package.