Patent Application
20130108207
Photonic integrated circuit (PIC) production processes typically include fabricating circuit elements such as modulators, switches, filters and so forth onto silicon and/or III V material wafers. These elements are connected during the process to form larger circuits such as switch arrays, modulator banks, optical add drop multiplexers, and so forth. Although complex chemical processes are involved in fabrication, often similar materials are typically employed when fabricating the wafers. These materials can include semiconductor materials such as silicon as a platform and for optical waveguide formation, III-V materials but also different types of electro-optical polymers or ferroelectric materials.
After the configurable material 130 has been activated in response to the electric field provided by the poling rails 140 and 150, the poling rails can be removed during fabrications, such as in a subsequent etching process (e.g., wet etching, plasma etching, or the like). It is noted that activation as used herein can include substantially any type of integrated circuit fabrication process where poling rails 140 and 150 provide some form of permanent or semi-permanent configuration to the circuit elements 120 within the integrated circuit 110. For example, the poling rails 140 and 150 could provide an electrical voltage activation, electrical current activation, electro-magnetic activation, or thermal activation such as establishing a thermal gradient between the rails (e.g., applying a heated probe to the poling rail). The configurable material 130 can include substantially any material that requires configuration during fabrication of the underlying integrated circuit wafer (e.g., before wafer has been separated into individual chips that are subsequently packaged) and is activated via the poling rails 140 or 150.
In general, each circuit element 120 can be connected to the poling rails 140 and 150 via circuit connections 160 and 170. Thus, the circuit connections 160 and 170 can serve a dual purpose. For example, during production of the integrated circuit 110, such connections can be employed with the poling rails 140 and 150 to activate the configurable material 130. After the configurable material 130 has been activated and the poling rails 140 and 150 have been removed, the circuit connections 160 and 170 can further be employed for desired circuit operations of the circuit element 120 and integrated circuit 110. The circuit connections 160 and 170 can be connected to integrated circuit pins for electrical connections to external components and/or can be connected to other connections within the integrated circuit 110, for example.
Although two poling rails 140 and 150 can be employed to configure a plurality of circuit elements 120 in parallel and as part of an efficient, batch production process, in other examples, a single rail could be utilized or more than two poling rails could be used for a larger circuit structure. For example, if a common connection were employed between a plurality of circuit elements 120, such common connection could be utilized in conjunction with a single poling rail (e.g., 140 or 150) to provide a path for activation to the configurable material 130.
As a further example, the integrated circuit 110 can be produced according to a method for fabricating a circuit element 120 and a connection 160 and 170 to the circuit element for the integrated circuit. This process can include associating a configurable material 130 with the circuit element 120 and activating the configurable material via a poling rail 140 or 150 and connection to the circuit element during production of the integrated circuit 110. As noted previously, the poling rail 140 or 150 can be removed after the configurable material 130 is activated. The poling rails 140 and 150 can be a metallic material or a doped semiconductor material, for example.
In the example of polymer as the configurable material 130, an electric field can be applied via the poling rails 140 and 150 and via the connections 160 and 170 to the circuit element 120 to activate the configurable material. This can include applying the electric field at an elevated temperature (e.g., greater than 100 deg C.) to activate the configurable material, which is subsequently cooled. After the polymer has been activated, it may be employed in an underlying circuit element function. This function can vary depending on the configuration of the circuit element, including the configurable material. In one example, the circuit element can be a photonic circuit (e.g., an optical waveguide, modulator, switch or the like), such that the structure comprising the configurable material can control its optical properties, such as its index of refraction or absorption properties. By configuring the material 130 in this way, the corresponding functionality of the circuit elements (e.g., switches, waveguides, gates, modulators, and/or filters) can be selectively enabled for corresponding operation, for example. In order that the poling rails 140 and 150 can be utilized for parallel activation processes of multiple circuit elements 120, path lengths for the connections 160 and 170 may have to be adjusted to the circuit element in order to accommodate a parallel connection. For instance, the path length connections for one circuit element may be longer or shorter than another circuit element to accommodate a parallel connection to the polling rails for multiple circuit elements.
Use of the poling rails 140 and 150 can facilitate batch and hence low cost processing of integrated circuit wafers that may need to have a plurality of circuit elements configured in some manner during fabrication. For example, such wafers can include silicon-based photonics integrated circuits (PICs), where silicon technology can be augmented in functionality by adding configurable materials, such as electro-optic polymers or other active materials (e.g., III-Vs, chalcogenides). These materials enable fabrication of circuit elements including efficient modulators, switches, and tunable filters on a silicon platform, for example. Thus, manufacturers do not have to configure individual devices or chips, but rather can pole the electro-optic polymer over an entire wafer, if desired, to facilitate efficient parallel configuration. Therefore, irrespective of the layout of the individual chip electronic control lead network on the wafer, manufacturing operations can still utilize the same circuit connections 160 and 170 for poling, given that they are connected to poling rails 140 and 150 such that in situ poling can occur in one process step. After etching away the poling rails 140 and 150, the wafer can be sectioned into chips for subsequent integrated circuit packaging.
For purposes of simplification of explanation, in the present example, different components of the system 100 are illustrated and described as performing different functions. However, one of ordinary skill in the art will understand and appreciate that the functions of the described components can be performed by different components, and the functionality of several components can be combined and executed on a single component.
During production processes however, the circuit connections 240 and 250 can be attached to the poling rails 210 and 220. During this phase, voltage can be applied via the poling rails 210 and 220, wherein polymer or other material within the control elements such as control element 230 is activated. In this example, a poling voltage can be applied to the electrodes via the poling rails 210 and 220. Such poling voltage can be applied to configure the polymer by orienting dipoles in the polymer in a similar direction and thus enabling desired optical properties such as the ability to control the index of refraction for light waves. After the activation process of the polymer, the poling rails 210 and 220 can be removed via an etching process. The circuit connections 240 and 250, which are initially employed for poling, can now be utilized for circuit operations of the integrated circuit 200 and can be connected to pins (not shown) for external connections that apply signals to operate the control elements. It is noted that application of poling can generally influence the manner in which the control wiring or lead arrangement in the integrated circuit 200 can be implemented, since the wiring should be compatible with poling as well as switch control (e.g., wiring arranged to allow parallel poling of multiple control elements).
It may not always be possible to apply the shortest route to the chip edge for the chip connections 240 and 250. For example, the connections 240 and 250 extend from each of a plurality of circuit elements 230 and terminate in a respective termination point (e.g., temporary termination point to make parallel connection to poling rail 210 or 220). However, at least some of the connections 240 or 250 can follow something different from a direct linear path (e.g., with lateral or zigzag extending portions) to couple to the poling rails 210 or 220. Since the connections 240 and 250 are designed to couple to respective poling rails, each of the termination points for a given poling rail can be aligned along a substantially linear path that remains even after the poling rails are removed. This substantially linear path is demonstrated schematically at 280 for poling rail 210 and at 290 for poling rail 220 and is substantially transverse to the direction that the connections extend.
Some of the electro-optic qualities of polymers will now be described but as noted above, the poling concepts described herein can be applied to substantially any type of material that requires configuration during production of the integrated circuit 200. Electro-optic polymers, for example polymers exhibiting Pockels linear electro-optic effect, provide one category of materials offering large refractive index changes in relation to other technology such as lithiumniobate. A figure of merit for such materials is the electro-optic coefficient (or r33-coefficient) being around 30 pm/V for lithium niobate and up to 500 pm/V for electro-optic polymers. With concomitant achievable index changes, such as larger than 0.1, this can lead to a decrease in the figure of merit voltage times length (V×L) product by orders of magnitude in relation to prevalent lithium niobate technology. In addition, since power scales as the voltage squared, there are possibilities to reduce power dissipation associated with charging and discharging capacitor electrodes such as controlling a modulator or switch as shown at 230. However, these materials generally require in situ poling, to transform them from inversion symmetry (r=0) to asymmetry and thus gaining the linear electro-optic effect.
Poling generally can occur at elevated temperatures, such as greater than 100 degrees C. (e.g., several hundred degrees C.), for example, using an electric field applied over the polymer via the poling rails 210 and 220. To enable low cost batch processing for each wafer containing many chips, it is thus desirable to use basically the same electrode pattern for poling as that used for controlling the photonic switch fabric and in general the on chip network. Such arrangement can be realized by connecting the intra-chip control electronic lead network (e.g., connections 240 and 250) to poling rails 210 and 220, such as at least two for each chip, connected in series for each row, and in parallel between rows as illustrated in
In view of the foregoing structural and functional features described above, an example method will be better appreciated with reference to
By way of further example the method 400 can also include fabricating the poling rail as a metallic material or as a doped semiconductor material, for example. This can include applying an electric field via the poling rail and the connection to the circuit element to activate the configurable material. The electric field can be applied at an elevated temperature to activate the configurable material. This can include a current, magnetic field, or a thermal gradient via the poling rail to activate the configurable material. If a polymer is employed as the configurable material, the underlying circuit element can be employed for controlling an index of refraction via the polymer after activation has occurred. The circuit element can be a switch, an optical waveguide, an optical gate, an optical modulator, or an optical filter, for example.
What have been described above are examples. It is, of course, not possible to describe every conceivable combination of components or methodologies, but one of ordinary skill in the art will recognize that many further combinations and permutations are possible. Accordingly, the disclosure is intended to embrace all such alterations, modifications, and variations that fall within the scope of this application, including the appended claims. As used herein, the term “includes” means includes but not limited to, the term “including” means including but not limited to. The term “based on” means based at least in part on. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements.
