Field
The present invention relates to micro devices. More particularly embodiments relate to a micro pick up array pivot mount with integrated strain sensing elements for aligning an electrostatic transfer head array with a target substrate.
Background Information
The feasibility of commercializing miniature devices such as radio frequency (RF) microelectromechanical systems (MEMS) microswitches, light-emitting diode (LED) display systems, and MEMS or quartz-based oscillators is largely constrained by the difficulties and costs associated with manufacturing those devices. Miniaturized device manufacturing processes typically include processes in which miniaturized devices are transferred from one wafer to another. In one such implementation, a transfer wafer may pick up an array of miniaturized devices from a donor wafer and bond the miniaturized devices to a receiving wafer. Methods and apparatuses for aligning two flat surfaces in a parallel orientation have been described, and may be applied to miniaturized device transfer.
A pivot mount and transfer tool are described. In an embodiment a pivot mount includes a pivot platform, a base, and a plurality of spring arms. Each spring arm is fixed to the pivot platform at a corresponding inner root, and fixed to the base at a corresponding outer root. Each spring arm also includes one or more switch-backs along an axial length of the spring arm such that a pair of first and second lengths of the spring arm immediately adjacent a switch-back are parallel to each other. A first strain sensing element may be located at the first length of the spring arm, and a second strain sensing element may be located at the second length of the spring arm. Likewise, a first reference gage may be located adjacent the first strain sensing element at the first length, and a second reference gage may be located adjacent the second strain sensing element at the second length. For example, the strain sensing elements may be strain gages that are bonded to the spring arm, deposited on the spring arm, or doped regions in the spring arm. In an embodiment, the plurality of spring arms includes three or more spring arms. In an embodiment, the one or more switch-backs includes an inner switch-back along an inner length of a spring arm, and an outer-switchback along an outer length of the spring arm.
In an embodiment, the inner root is perpendicular to an inner length of the spring arm extending from the pivot platform, and the outer root is perpendicular to an outer length of the spring arm extending from the base. In an embodiment, the pivot platform is movable relative to the base in a direction orthogonal to a contact surface of the pivot platform, and movement of the pivot platform in the direction orthogonal to the contact surface causes a normal strain at the surface of the spring arm that is characterized as being parallel to the axial length of the spring arm at the first and second lengths of the spring arm. In an embodiment, the normal strain at the surface of the spring arm is of opposite sign on the first and second lengths of the spring arm.
In an embodiment, a pivot mount includes a pivot platform with a plurality of compliant voltage contacts, a base, and a plurality of spring arms in which each spring arm is fixed to the pivot platform at a corresponding inner root and fixed to the base at a corresponding outer root. In an embodiment, each compliant voltage contact is at least partially formed by a channel extending through the pivot platform. The compliant voltage contacts may assume a variety of configurations including a winding contour and switch-back. In an embodiment, the pivot mount includes a clamping electrode on the pivot platform. Each compliant voltage contact may protrude from the pivot platform such that they are raised above the pivot platform and clamping electrode.
In an embodiment, any of the pivot mounts described above may be included in a transfer tool, including an articulating transfer head assembly, and a micro mick up array mounted onto the pivot platform of the pivot mount. The micro pick up array may include a plurality of electrostatic transfer heads. In an embodiment, the pivot platform includes a plurality of compliant voltage contacts as described above. The micro pick up array may include a plurality of voltage contacts arranged to mate with the plurality of compliant voltage contacts of the pivot platform. In an embodiment each electrostatic transfer head has a localized contact point characterize by a maximum dimension of 1-100 μm in both the x- and y-dimensions.
Embodiments describe a pivot mount including a base, a pivot platform, and plurality of spring arms, each spring arm including a switch-back along an axial length of the spring arm such that a pair of first and second lengths of the spring arm immediately adjacent the switch-back are parallel to each other. A first strain sensing element is located at the first length, and a second strain sensing element is located at the second length of the spring arm. In this manner, when the pivot mount is moved in a direction orthogonal to a contact surface of the pivot platform normal strains of opposite sign are created at the surface of the spring arm on the first and second lengths of each spring arm.
The pivot mount can be coupled to an articulating head assembly of a mass transfer tool for accurate and repeatable alignment in 6 spatial degrees of freedom between the transfer tool and a target substrate. When accurately aligning two planar surfaces, lateral (x and y) and rotational (θz) alignments are relatively straightforward to achieve through use of a high-precision x-y stage and rotationally-positioned substrate chucks. The remaining three degrees of freedom, θx, θy, (or, “tilt” and “tip”) and z are difficult to independently control. Any changes to the tip and tilt angle necessarily change the distance z to any point not located at the center of rotation. While parallelism between two planes can be accomplished through use of a passive pivot mount, the pressure distribution between the two planar surfaces will not be centered or uniform unless the two surfaces were parallel to begin with. A transfer tool including a pivot mount in accordance with embodiments described herein may redistribute the pressure distribution to achieve a uniform pressure field. By placing strain sensing elements (strain gages) at high-strain locations on the pivot mount spring arms, a feedback signal of the position error can be generated and input to the transfer tool for operation in a closed-loop motion control system. Because strain is related to the stress state through Hooke's Law, both displacement and forces acting on the pivot mount can be known by measuring strain.
In one aspect, embodiments describe a pivot mount configuration that achieves a high strain sensing sensitivity and generates a feedback signal with a high signal to noise ratio. As a result the pivot mount can provide a position feedback signal with increased effective resolution to the transfer tool. By locating the strain sensing elements on opposite sides of switch-backs in an axial length of a spring arm, equal and opposite strain responses are measured. In this manner a strain signal for a given platform displacement may be effectively doubled. Such a configuration can also reduce noise for a given strain signal. Due to the differential sensing at the first and second lengths adjacent the switch-back the measured noise is effectively canceled. Accordingly, higher strain sensing sensitivity may be accomplished with a higher signal to noise ratio, and an increased effective resolution of the position feedback signal may be provided to the transfer tool.
In another aspect, embodiments describe pivot mount spring arm configurations that minimize the torsion applied to a spring arm at the roots where a spring arm is fixed to a pivot platform at one end and fixed to a base at another end. This creates a more uniform bending moment in the high strain regions of the spring arm with reduced strain variation and torsion in the spring arms, which allows the strain sensing elements to be located in the high strain regions near the roots. By comparison, in other configurations with spring arms that undergo both bending and torsional loading, the area of maximum strain may include both bending and torsion. Torsion in the spring arms is parasitic to surface strain sensing since it manifests as strain at the surface of the spring arm having components in both the x and y directions. Because the total strain energy distributed through the spring arms is constant for a given pivot platform displacement, the presence of strain components perpendicular to the strain sensing elements reduces the ratio of strain components that are aligned with the strain sensing elements. As a result, strain sensing elements located near areas of torsion may produce a lower effective feedback signal and sensitivity. In an embodiment, a pivot mount is arranged to create boundary conditions at the roots of the spring arms with a uniform bending moment, in which strain is substantially perpendicular to the roots and substantially parallel to strands in the strain sensing elements, which may be parallel to axial lengths of the spring arms in the high strain regions. Such a configuration directs substantially all of the strain energy from a given pivot platform displacement into strain components aligned with the strain sensing elements. As a result, higher strain may be measured and sense feedback signal strength may be increased for a given pivot platform displacement. Reduction of the torsional moment at the roots may additionally allow more freedom in stiffness requirements of the spring arms. In turn, reduced stiffness requirements allow for longer axial length of the spring arms in the same available real estate within the pivot mount, and consequently greater bending, resulting in increased normal strain at the surface of the spring arms and sense feedback signal strength.
In another aspect, reduction of the torsional moment applied to the spring arms at the roots may also increase the effectiveness of the reference gage(s) positioned adjacent the strain sensing elements. In an embodiment, each strain sensing element is located in a high strain region of a spring arm that sees only normal strain at the surface in the gage direction of the strain sensing element and sees no normal strain at the surface lateral to the gage direction. This allows the location of a reference strain gage adjacent to each strain sensing element with the result that the reference gages do not see strain caused by mechanical loading of the pivot platform. This in turn allows the reference gages to compensate for temperature variations in the system, and increase the signal to noise ratio. Since the strain sensing elements and reference gages are adjacent, they are exposed to the same temperature, meaning the thermal strain is identical in both a strain sensing element and a corresponding reference gage. Since the reference strain gages are not subjected to strain resulting from mechanical load, any strain signal they produce can be attributed to temperature (as noise), which is then subtracted as background noise from the strain measured by the adjacent strain sensing element. In an embodiment, strands in the reference gages are oriented perpendicular to strands in the strain sensing elements. In such a configuration, the normal strain at the surface of the spring arms is substantially parallel to the strands in the strain sensing elements, and perpendicular to the strands in the reference strain gages. Thus, by reducing the torsional moment and creating uniform bending moments in the spring arms in which normal strain at the surface of the spring arms is substantially perpendicular to the roots, the reference strain gages may be more accurate and a higher strain sensing sensitivity may be accomplished with a higher signal to noise ratio.
In another aspect, embodiments describe an arrangement of strain sensing elements into distributed, correlated sensors. In this manner, the loss of a strain sensing element or sensor does not prohibit use of the pivot mount, and the lifetime of the pivot mount use with a transfer tool can be extended. In an embodiment, each sensor includes one or more correlation sensors. For example, a correlated pair may each sense a same z-deflection. In another situation, a correlated pair may sense a same or equal but opposite θx, θy, (or, “tilt” and “tip”). In either situation, the loss of one of the correlated sensor may reduce the overall signal to noise ratio generated from the pivot platform, yet the remaining signal to noise ratio remains adequate for operation of the transfer tool.
In yet another aspect, embodiments describe a pivot mount with compliant voltage contacts, for providing a low contact resistance connections of the voltage contacts to a micro pick up array (MPA) that is mounted onto the pivot platform of the pivot mount. The compliant voltage contacts may protrude from the pivot platform such that they are elevated above the pivot platform, yet are compliant such that they exert a pressure upon the MPA contacts when the MPA is clamped onto the pivot mount pivot platform, for example, using an electrostatic clamp contact on the pivot mount platform.
Referring to
Referring to
As illustrated, the pivot mount 300 may include a base 302, a pivot platform 304, and plurality of spring arms 306, and the MPA 103 supporting a transfer head array 115 is mounted on the pivot platform 304. In an embodiment, the transfer head array 115 is an electrostatic transfer head array 115, where each transfer head operates in accordance with electrostatic principles to pick up and transfer a corresponding micro device. In an embodiment each electrostatic transfer head has a localized contact point characterized by a maximum dimension of 1-100 μm in both the x- and y-dimensions. In an embodiment, the pivot mount 300 may communicate and send feedback signals to the mass transfer tool 100 through one or more electrical connections, such as a flex circuit 308. As described below, feedback may include analog signals from strain sensing elements that are used in a control loop to regulate actuation and spatial orientation of the transfer head assembly 200. In an embodiment, the feedback signals are sent to a position sensing module located near the pivot mount 300 to reduce signal degradation by limiting a distance that analog signals must travel from a strain sensing element to the position sensing module. In an embodiment, the position sensing module is located within the transfer head assembly 200.
Referring now to
As illustrated in
Referring now to
Referring now to
Referring again to
Referring now to
Referring now to both
Wiring 380, 382, and 384 may be routed to an electrical connection, such as a flex circuit 308, at an edge of the base 302 of the pivot mount. For example, an operating voltage can be applied trough the flex circuit 308 to operate the electrostatic clamp contacts 318 to clamp the MPA onto the pivot mount 300. Another operating voltage can be applied through the flex circuit 308 to operate the compliant voltage contacts 316 which transfer an operational voltage to the array of electrostatic transfer heads in order to provide a grip pressure to pick up micro devices. Additionally, the flex circuit 308 can transfer the feedback signals from the strain sensing elements 320 and reference gages 340 to a position sensing module or computer 108 to regulate actuation and spatial orientation of the transfer head assembly 200.
Referring now to
A strain gage may be separately formed from spring arm 306 and attached thereto. In an embodiment, the strain gage includes an insulative flexible backing that supports a foil formed from polysilicon and electrically insulates the foil from spring arm 306. The foil may be arranged in a serpentine pattern, for example. An example of an attachable strain gage is a Series 015DJ general purpose strain gage manufactured by Vishay Precision Group headquartered in Malvern, Pa. A strain gage that is separately formed from spring arm 306 may be attached to spring arm 306 using numerous processes. For example, the strain gage backing may be directly attached to spring arm 306 with an adhesive or other bonding operation. More specifically, strain gage backing may be fixed to a surface of spring arm 306 using solder, epoxy, or a combination of solder and a high-temperature epoxy.
In another embodiment, a strain gage may be formed on spring arm 306 in a desired pattern, such as a serpentine pattern. In an embodiment, a strain gage may be formed directly on spring arm 306 using a deposition process. For example, constantan copper-nickel traces may be sputtered directly on spring arm 306 in a serpentine pattern. The dimensions of a strand of a sputtered strain gage having a serpentine pattern may be about 8 micron width with about an 8 micron distance between strand lengths and may be deposited to a thickness of about 105 nanometers.
In another embodiment, the material of spring arm 306 may be modified to form an integrated strain gage. More specifically, spring arm 306 may be doped with a piezoresistive material to create a strain gage within spring arm 306. As an example, the surface of spring arm 306 may be doped silicon. The doped material may be in a serpentine pattern, having dimensions that vary with an applied strain. Thus, the strain gage may be fully integrated and physically indistinct from the remainder of spring arm 306.
During the transfer of micro devices from a carrier substrate, spring arm 306 and strain sensing elements 320 may be subjected to elevated temperatures, and thus, temperature compensation may be necessary. In an embodiment, strain sensing element 320 (strain gage) may be self-temperature compensated. More specifically, strain gage material may be chosen to limit temperature-induced apparent strain over the operating conditions of the transfer process. However, in an alternative embodiment, other manners for temperature compensation may be used. For example, temperature compensation may be achieved using a reference gage technique.
In an embodiment, strain sensing element 320 may be a strain gage on spring arm 306 having a pattern (e.g. serpentine) of lengthwise strands that align in a direction of anticipated normal strain at the surface of the spring arm. Still referring to
In particular, the strands 341 in the references gages 340 are oriented perpendicular to strands 321 in the strain sensing elements 320. As will become more apparent in the following description, the normal strain at the surface that results at the first and second lengths 364, 366 of the spring arm during operation of the pivot mount is substantially parallel to the strands 321 in the strain sensing elements, and perpendicular to the strands 341 in the reference strain gages. Similar strain relationships are found at all of the inner switch-backs 356 and outer switch-backs 358, wherein normal strain at the surface that occurs during operation of the pivot mount is substantially parallel to the strands in the strain sensing elements 320.
Referring now to
Referring now to
In order to illustrate strain confinement within the pivot mount, a pivot mount with a uniform z displacement of the pivot platform 304 is illustrated in
In accordance with embodiments of the invention, a pivot mount structure achieves a high strain sensing sensitivity and generates a feedback signal with a high signal to noise ratio by locating strain sensing elements on opposite sides of switch-backs in an axial length of a spring arm, where equal and opposite strain responses are measured. In this manner, strain signal for a given platform displacement may be effectively doubled, while also reducing noise for a given strain signal since the differential sensing can be used to effectively cancel the noise.
Referring to
Referring to
Strain sensing elements 320 and reference gages 340 may be arranged into sensors so that the resulting sensor signals are correlated. A set of sensors is considered correlated, or dependent, if the signal of a missing or broken gage in the sensor may be approximated from the remaining set of signals. A minimum set of independent strain signals equal to the number of desired position measurements is required to calculate those measurements. Correlated strain signals in excess of the minimum required set may be included in the position calculation and used to improve the signal to noise ration of the measurement. If a strain gage (320, 340) or sensor failure occurs the calculation may be adjusted to maintain position output albeit with a reduced signal to noise ratio. In this way correlated signals provide redundancy as well as an improved signal to noise ratio. Referring to
In the above exemplary embodiment, several correlated pairs are described for an 8 channel (signal) operation, with each channel corresponding to a signal produced by a pair of strain gages and references gages adjacent a switch-back. Under normal operation, the feedback signal produced by the exemplary pivot mount operating under normal operation can be converted into a synthesized output signal by transformation matrix equation (1):
While embodiments of pivot mounts have been described thus far in a square configuration, with switch-backs located along the x-direction or y-direction, embodiments are not so limited. Indeed, the strain sensing elements and reference gages can be located along a number of directions. A generalized transformation matrix for converting a pivot mount feedback signal to a synthesized output signal is represented in equation (2) for n strain signal inputs to 3 position measurement outputs (e.g. tilt, tip, z):
In an embodiment illustrated in
In accordance with embodiments of the invention, the transfer head assembly 200 may adjust the orientation of the MPA 103 until a desired amount of and/or a desired distribution of pressure across pivot mount 300 is sensed by the pivot mount 300 strain sensing elements 320. Thus, the transfer head array 115 on MPA 103 may be actively aligned with an array of micro devices on a mating substrate. For example, the spatial orientation representing alignment may be predetermined to include a plane passing through the transfer head array 115 being parallel to a plane passing through the array of micro devices. Alternatively, the spatial orientation representing alignment may include the planes not being parallel, but rather, being in some predetermined mutual orientation, such as angled such that only a portion of the transfer head array 115 make contact with respective micro devices when the arrays are brought together. More particularly, the spatial orientation representing alignment of the transfer head array 115 with the array of micro devices may be any predetermined spatial orientation. Such spatial orientation may be monitored, sensed, and measured to determine system characteristics such as distribution of pressure across pivot mount 300. Thus, the measured system characteristics may be used as a proxy to represent alignment. Active alignment may increase the transfer rate of micro devices, since fine-alignment may be accomplished while picking up, and similarly while releasing, the micro devices. Furthermore, active alignment may be made on-the-fly without parasitic translation of the transfer head array 115 that may otherwise smear and damage the array of micro devices. Such on-the-fly adjustments may be useful when a donor substrate, e.g., carrier substrate, and/or a display substrate, e.g., receiving substrate, include surface irregularities and non-planar contours.
Referring to
A primary input 1302 may define a set of reference signals that correspond to an initial desired state of MPA 103. More specifically, primary input 1802 may define a target spatial location of MPA 103 relative to an anticipated location of a micro device array or substrate surface. Primary input 1302 may be fed into one of several inner loops, each of which may correspond to an individual actuator. For example, x-actuator inner loop 1304 may correspond to a control loop for controlling an x-actuator of the transfer head assembly, and thus MPA 103, to tip about a remote rotational center. Similarly, y-actuator inner loop 1306 may correspond to a control loop for controlling a y-actuator of the transfer head assembly, and thus MPA 103, to tilt about the remote rotational center. Also, z-actuator inner loop 1308 may correspond to a control loop for controlling a z-actuator of the transfer head assembly and thus a location of MPA 103 along a z-axis. Therefore, the combination of inner loops allow for the control of actuators that adjust a tip, tilt, and z-spatial orientation of MPA 103.
In an embodiment, inner loop control of transfer head assembly 200 actuators results in a primary output 1310. More specifically, primary output 1310 may be an instantaneous geometric configuration of transfer head assembly 200 resulting from actuator movement. The geometric configuration may be inferred from data supplied by encoders or other sensors that track spatial position of individual transfer head assembly 200 components. That is, the geometric configuration may include a combination of individual geometric configurations such as a tip position, tilt position, and z-position. Primary output 1310 may also relate to a spatial position of MPA 103 as inferred from known physical dimensions of transfer head assembly 200 components. Alternatively, MPA 103 surface location may be sensed directly using, e.g., laser micrometers, accelerometers, etc., to provide spatial orientation feedback that may be included directly in primary output 1310. Thus, a position of MPA 103 may be inferred or sensed to determine whether primary output 1310 has been achieved, i.e., equals the intended primary input 1302. However, although MPA 103 may be driven toward a target substrate to achieve the positional command of primary input 1302, in some cases, MPA 103 may contact the target substrate. Furthermore, once contact is detected, primary input 1302 may be modified by additional commands from several actuator outer loops, to achieve a neutral tip and tilt deformation of pivot mount 300 with a desired pressure distribution across pivot mount 300. Accordingly, MPA array 103 may be driven to a tip deflection, tilt deflection, and z-compression target within an accuracy in the submicron range, e.g., on the order of less than about 250 nm.
After contact between a transfer head array 115 of MPA 103 and a micro device has been made, MPA 103 may be finely adjusted based on pressure feedback from the pivot mount 300. More particularly, fine adjustment of MPA 103 may be enabled in response to system recognition of a contact disturbance 1312. In an embodiment, enable logic is included to determine whether a contact disturbance 1312 is sensed prior to MPA 103 achieving the desired primary input 1302, and if a contact disturbance 1312 is sensed, additional control loops may be closed to permit fine adjustment of the transfer head assembly 200. More specifically, additional control loops may be closed to drive MPA 103 toward tip deflection, tilt deflection, and z-compression targets, rather than toward the initial positional target of primary input 1302.
In an embodiment, a contact disturbance 1312 is sensed when, e.g., MPA 103 contacts a mating substrate out of alignment. For example, if MPA 103 and the mating substrate make contact in perfect alignment, the primary output 1810 may equal the primary input 1802 and micro devices may then be gripped by transfer head array 115 without requiring additional adjustment. However, if MPA 103 and the mating substrate are not perfectly aligned, displacement or strain measurements from each strain sensing element 320 on pivot mount 300 may be substantially different from each other and/or the desired level of pressure may not be achieved. That is, in an embodiment, an expected or desired tip, tilt, and compression state must be satisfied prior to initiating electrostatic gripping. If the desired state is not achieved, displacement or strain measurements may be fed as feedback signals 1314.
In an embodiment, feedback signals 1314 correspond to analog signals from the strain sensing elements 320 and references gages 340. In the exemplary embodiment above, feedback signals 1314 may include eight sensor signals from sixteen separate strain sensing elements 320 and sixteen reference gages 340. The feedback signals 1314 may be conditioned by a signal conditioning and combination logic 1315 to transform the analog signals into a synthesized output signal representing a strain state of a respective strain sensing element. These synthesized output signals may furthermore be combined by signal conditioning and combination logic 1315 to synthesize one or more of a pivot mount 300 compression synthesized output signal, a pivot mount 300 tilt deflection synthesized output signal, and a pivot mount 300 tip deflection synthesized output signal represented by a transformation matrix equation, such as equation (1) or equation (2) described above. The synthesized output signals may be provided as inputs to dynamic control enable logic 1316. More particularly, dynamic control enable logic 1316 may observe the one or more synthesized output signals to determine that a contact disturbance 1312 has occurred in one or more of a tip, tilt, or z-direction. For example, if a non-zero compression signal is synthesized by signal conditioning and combination logic 1315 that exceeds predetermined limits, dynamic control enable logic 1316 may recognize the contact disturbance 1312.
In response to observing that a contact disturbance 1312 exists, dynamic control enable logic 1316 may close respective outer loops, each of which may be configured to provide output commands to modify the positional command of primary input 1302. Thus, closing the outer loops may drive the actuators to achieve a desired state of pressure and orientation, rather than driving them to achieve an initial position command. For example, if dynamic control enable logic 1316 observes that a compression contact disturbance 1312 exists, z-actuator outer loop 1318 may be closed to respond to the contact disturbance 1312 by adjusting a z-actuator. Likewise, dynamic control enable logic 1316 may respond to tip deflection signals or tilt deflection signals by enabling x-actuator outer loop 1320 or y-actuator outer loop 1322, respectively.
Deflection and compression feedback signals may be passed from signal conditioning and combination logic 1315 as synthesized output signals to respective outer loops for comparison with deflection command inputs 1340 provided to respective outer loops. In an embodiment, pivot mount 300 deflection command inputs 1340 may correspond to a desired pressure distribution across pivot mount 300 or MPA 103. Thus, pivot mount 300 deflection command inputs 1340 may represent tip deflection, tilt deflection, and z-compression targets of pivot mount 300. These targets may be compared to the synthesized output signals from signal conditioning and combination logic 1315, which indicate an instantaneous pressure distribution across pivot mount 300, to determine a difference. The difference, if any, may then be fed as an error signal to drive respective transfer head assembly 200 actuators. For example, if tipping of pivot mount 300 is sensed as a contact disturbance 1312 and dynamic control enable logic 1316 observes that the tipping exceeds an allowable amount, x-actuator outer loop 1320 may be closed and the tipping deflection signal may be compared with a pivot mount 300 tip deflection command 1340 to generate a motion control signal that will tip pivot mount 300 toward a desired stress state. The motion control signal may be fed to a servo filter and passed through inverse kinematics calculations to generate an outer loop command output 1330. In an embodiment, the motion control signal may also be added with other transfer head assembly motion control signals at one or more of motion summation nodes 1350. This may be the case, for example, when movement of multiple actuators is required to cause tipping.
In order to close the control loop, the outer loop command outputs 1330 may be combined with primary input 1302 and passed back into actuator inner loops. For example, a tipping outer loop command 1330 may be summed with primary input 1302 for an x-actuator and passed through x-actuator inner loop 1304, thereby controlling an x-actuator in such a manner that pivot mount 300 tips toward a physical state of more even pressure distribution. Respective outer loop commands may be passed through to any actuator inner loop for which a contact disturbance 1312 was sensed.
The above control methodology may be performed and repeated until the transfer head assembly 200 is moved to a location at which pressure distribution across pivot mount 300, and hence MPA 103, is uniform and achieves a desired amount of pressure. Thus, transfer head assembly 200 may be controlled to bring an array of electrostatic transfer head array 115 on MPA 103 into contact with an array of micro devices on a mating substrate. Using the control system described above, if alignment between MPA 103 and the mating substrate is not initially perfect, which would be true of almost every transfer operation, pressure distribution control may be implemented to fine tune the alignment. The control methodology may be performed quickly, e.g., on the order of about 50 ms to sense a contact disturbance 1312, enable the appropriate outer loop(s), and feed appropriate outer loop control commands to actuators, and thus, complete contact may be rapidly achieved between an electrostatic transfer head array 115 and an array of micro devices, enabling efficient transfer between a carrier substrate and a receiving substrate.
Referring now to
Referring to the embodiment illustrated in
Examples of generating a synthesized output signal utilizing the 8 channel embodiment of
Referring to
Initially, there may be no compressive loading applied to MPA 103 or pivot mount 300. This initial state may correspond to a range of travel over which array of micro devices are physically separated from the electrostatic transfer head array. During this travel, MPA 103 and the target substrate may have misaligned surfaces, but there may be no indication of this misalignment since the pressure distribution state of pivot mount 300 may be uniform, i.e., all strain sensing elements may be outputting signals indicating zero strain.
At operations 1404 and 1406, an electrostatic transfer head in the electrostatic transfer head array 115 may contact a micro device while other electrostatic transfer heads may remain separated from corresponding micro devices. That is, contact may be made while MPA 103 is misaligned with the target substrate. This positional misalignment may be sensed as uneven pressure distribution in pivot mount 300. For example, a first strain output value from one strain sensing element 320 on pivot mount 300 and a different second strain output value from another strain sensing element 320 in pivot mount 300 may differ. The strain signals may be provided as feedback signals 1314 and conditioned and combined by into synthesized output signals (e.g. tip deflection, tilt deflection, and compression signals) by signal conditioning and combination logic 1315 indicating a contact disturbance 1312.
Dynamic enable control logic 1316 may observe that the contact disturbance 1312 exists, and depending upon the level of contact disturbance 1312, may activate actuator outer loops to determine driving signals for actuating various actuators of transfer head assembly 200 in order to adjust an orientation of MPA 103 such that pressure distribution across pivot mount 300 is uniform. For example, at operation 1408, in response to the tip signal being recognized as a contact disturbance 1312 above a threshold, x-actuator outer loop 1320 may feed command signals 1330 to x-actuator inner loop 1304 in order to actuate an x-actuator to tip MPA 103 about remote rotational center. Similarly, at operation 1410, in response to the tilt deflection signal being recognized as a contact disturbance 1312 above a threshold, y-actuator outer loop 1322 may feed command signals to y-actuator inner loop 1306 in order to actuate a y-actuator 708 to tile MPA 103 about remote rotational center.
At operation 1412, in response to actuation of the x- and y-actuators based on the tip and tilt deflection signals MPA 103 may be rotated into alignment with the target substrate. Furthermore, with remote rotational center co-located with the contact surface of MPA 103, the electrostatic transfer head array 115 may experience pure rotation about remote rotational center. Thus, as MPA 103 is aligned with the target substrate, the electrostatic transfer head array 115 may experience minimal parasitic lateral motion and micro devices may remain undamaged.
Actuation of transfer head assembly 200 according to synthesized output signals (tip, tilt, and z-compression signals) may continue until the electrostatic transfer head array 115 is in contact with micro devices on the target substrate. More particularly, actuation may continue until primary output 1310 is within the limits set by primary input 1302, at which point actuation may be stopped. As discussed above, primary output 1310 may be a positional output that is modified to reach a desired pivot mount 300 state. For example, actuation of transfer head assembly 200 may continue until primary positional input is achieved and/or pressure distribution across pivot mount 300 is uniform.
After contact between the electrostatic transfer head array 115 and the micro devices is made, a voltage may be applied to the electrostatic transfer head array 115 to create a grip pressure on the array of micro devices. An electrostatic voltage may be applied to electrostatic transfer head array 115 compliant voltage contacts 316 and voltage contacts 120. Additional electrical contacts and connectors may be integrated within transfer head assembly 200 and powered by voltage supplies based on control signals from computer 108. For example, computer 108 may implement a control algorithm instructing that electrostatic transfer head array 115 be activated if a predefined deformation is simultaneously sensed by each displacement sensor on pivot mount 300 during a pick up process. As a result, the array of electrostatic transfer head array 115 may apply a gripping pressure to the array of micro devices after the entire array surface is in contact and uniform pressure is applied across the array.
After gripping the micro devices with electrostatic transfer head array 115, the micro devices may be picked up from carrier substrate. During pick up, the electrostatic voltage supplied to the electrostatic transfer head array 115 may persist, and thus, the array of micro devices may be retained on the electrostatic transfer head array 115 and removed from the carrier substrate.
During the pick up operation, a heating element may direct heat toward pivot mount 300 and/or MPA 103. Thus, the micro devices may be heated through contact with electrostatic transfer head array 115 on MPA 103 during pick up. For example, a heating element adjacent to pivot mount 300 may be resistively heated to transfer heat to MPA 103, and thus, to the micro devices through the electrostatic transfer head array 115. Heat transfer may occur before, during, and after picking up the array of micro devices from carrier substrate.
Although a pick up process is described in relation to
Referring to
Computer 108 of
The data storage device 1510 may include a non-transitory machine-readable storage medium 1518 on which is stored one or more sets of instructions (e.g. software 1520) embodying any one or more of the methodologies or operations described herein. For example, software 1520 may include instructions, which when executed by processor 1504, cause computer 108 to control mass transfer tool 100 or remote center robot 500 according to the control scheme described above for aligning an MPA 103 with a target substrate. Software 1520 may also reside, completely or at least partially, within the volatile memory, non-volatile memory 1508, and/or within processor 1504 during execution thereof by computer 108, volatile memory 1506, non-volatile memory 1508, and processor 1504 also constituting non-transitory machine-readable storage media.
In utilizing the various aspects of this invention, it would become apparent to one skilled in the art that combinations or variations of the above embodiments are possible for forming a pivot mount with integrated strain sensing elements and/or compliant voltage contacts. Although the present invention has been described in language specific to structural features and/or methodological acts, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific features or acts described. The specific features and acts disclosed are instead to be understood as particularly graceful implementations of the claimed invention useful for illustrating the present invention.
This application is a continuation of co-pending U.S. patent application Ser. No. 14/303,483, filed Jun. 12, 2014, which is incorporated herein by reference.
Number | Name | Date | Kind |
---|---|---|---|
3717743 | Costello | Feb 1973 | A |
3935986 | Lattari et al. | Feb 1976 | A |
5131582 | Kaplan et al. | Jul 1992 | A |
5378926 | Chi et al. | Jan 1995 | A |
5435857 | Han et al. | Jul 1995 | A |
5592358 | Shamouilian et al. | Jan 1997 | A |
5740956 | Seo et al. | Apr 1998 | A |
5794839 | Kimura et al. | Aug 1998 | A |
5839187 | Sato et al. | Nov 1998 | A |
5851664 | Bennett et al. | Dec 1998 | A |
5888847 | Rostoker et al. | Mar 1999 | A |
5903428 | Grimard et al. | May 1999 | A |
5996218 | Shamouilian et al. | Dec 1999 | A |
6071795 | Cheung et al. | Jun 2000 | A |
6080650 | Edwards | Jun 2000 | A |
6081414 | Flanigan et al. | Jun 2000 | A |
6335263 | Cheung et al. | Jan 2002 | B1 |
6403985 | Fan et al. | Jun 2002 | B1 |
6420242 | Cheung et al. | Jul 2002 | B1 |
6521511 | Inoue et al. | Feb 2003 | B1 |
6558109 | Gibbel | May 2003 | B2 |
6613610 | Iwafuchi et al. | Sep 2003 | B2 |
6629553 | Odashima et al. | Oct 2003 | B2 |
6670038 | Sun et al. | Dec 2003 | B2 |
6683368 | Mostafazadeh | Jan 2004 | B1 |
6786390 | Yang et al. | Sep 2004 | B2 |
6878607 | Inoue et al. | Apr 2005 | B2 |
6918530 | Shinkai et al. | Jul 2005 | B2 |
7033842 | Haji et al. | Apr 2006 | B2 |
7148127 | Oohata et al. | Dec 2006 | B2 |
7208337 | Eisert et al. | Apr 2007 | B2 |
7353596 | Shida et al. | Apr 2008 | B2 |
7358158 | Aihara et al. | Apr 2008 | B2 |
7439549 | Marchl et al. | Oct 2008 | B2 |
7585703 | Matsumura et al. | Sep 2009 | B2 |
7628309 | Erikssen et al. | Dec 2009 | B1 |
7714336 | Imai | May 2010 | B2 |
7723764 | Oohata et al. | May 2010 | B2 |
7795629 | Watanabe et al. | Sep 2010 | B2 |
7797820 | Shida et al. | Sep 2010 | B2 |
7838410 | Hirao et al. | Nov 2010 | B2 |
7854365 | Li et al. | Dec 2010 | B2 |
7880184 | Iwafuchi et al. | Feb 2011 | B2 |
7884543 | Doi | Feb 2011 | B2 |
7888690 | Iwafuchi et al. | Feb 2011 | B2 |
7906787 | Kang | Mar 2011 | B2 |
7910945 | Donofrio et al. | Mar 2011 | B2 |
7927976 | Menard | Apr 2011 | B2 |
7928465 | Lee et al. | Apr 2011 | B2 |
7972875 | Rogers et al. | Jul 2011 | B2 |
7989266 | Borthakur et al. | Aug 2011 | B2 |
7999454 | Winters et al. | Aug 2011 | B2 |
8023248 | Yonekura et al. | Sep 2011 | B2 |
8076670 | Slater et al. | Dec 2011 | B2 |
8186568 | Coronel et al. | May 2012 | B2 |
8333860 | Bibl et al. | Dec 2012 | B1 |
8349116 | Bibl et al. | Jan 2013 | B1 |
8426227 | Bibl et al. | Apr 2013 | B1 |
8518204 | Hu et al. | Aug 2013 | B2 |
9391042 | Golda et al. | Jul 2016 | B2 |
9624100 | Bathurst | Apr 2017 | B2 |
20010029088 | Odajima et al. | Oct 2001 | A1 |
20020076848 | Spooner et al. | Jun 2002 | A1 |
20030010975 | Gibb et al. | Jan 2003 | A1 |
20030177633 | Haji et al. | Sep 2003 | A1 |
20040100164 | Murata et al. | May 2004 | A1 |
20040232439 | Gibb et al. | Nov 2004 | A1 |
20040266048 | Platt et al. | Dec 2004 | A1 |
20050224822 | Liu | Oct 2005 | A1 |
20050232728 | Rice et al. | Oct 2005 | A1 |
20060038291 | Chung et al. | Feb 2006 | A1 |
20060055035 | Lin et al. | Mar 2006 | A1 |
20060065905 | Eisert et al. | Mar 2006 | A1 |
20060157721 | Tran et al. | Jul 2006 | A1 |
20060160276 | Brown et al. | Jul 2006 | A1 |
20060214299 | Fairchild et al. | Sep 2006 | A1 |
20070048902 | Hiatt et al. | Mar 2007 | A1 |
20070166851 | Tran et al. | Jul 2007 | A1 |
20070194330 | Ibbetson et al. | Aug 2007 | A1 |
20070284604 | Slater et al. | Dec 2007 | A1 |
20080048206 | Lee et al. | Feb 2008 | A1 |
20080150134 | Shinkai et al. | Jun 2008 | A1 |
20080163481 | Shida et al. | Jul 2008 | A1 |
20080194054 | Lin et al. | Aug 2008 | A1 |
20080196237 | Shinya et al. | Aug 2008 | A1 |
20080205027 | Coronel et al. | Aug 2008 | A1 |
20080283190 | Papworth et al. | Nov 2008 | A1 |
20080283849 | Imai | Nov 2008 | A1 |
20080303038 | Grotsch et al. | Dec 2008 | A1 |
20090068774 | Slater et al. | Mar 2009 | A1 |
20090072382 | Guzek | Mar 2009 | A1 |
20090146303 | Kwon | Jun 2009 | A1 |
20090242918 | Edmond et al. | Oct 2009 | A1 |
20090303713 | Chang et al. | Dec 2009 | A1 |
20090314991 | Cho et al. | Dec 2009 | A1 |
20100052004 | Slater et al. | Mar 2010 | A1 |
20100105172 | Li et al. | Apr 2010 | A1 |
20100123164 | Suehiro et al. | May 2010 | A1 |
20100176415 | Lee et al. | Jul 2010 | A1 |
20100188794 | Park et al. | Jul 2010 | A1 |
20100200884 | Lee et al. | Aug 2010 | A1 |
20100203659 | Akaike et al. | Aug 2010 | A1 |
20100203661 | Hodota | Aug 2010 | A1 |
20100213471 | Fukasawa et al. | Aug 2010 | A1 |
20100214777 | Suehiro et al. | Aug 2010 | A1 |
20100248484 | Bower et al. | Sep 2010 | A1 |
20100257934 | Zhang et al. | Oct 2010 | A1 |
20100276726 | Cho et al. | Nov 2010 | A1 |
20110001145 | Park | Jan 2011 | A1 |
20110003410 | Tsay et al. | Jan 2011 | A1 |
20110049540 | Wang et al. | Mar 2011 | A1 |
20110132655 | Horiguchi et al. | Jun 2011 | A1 |
20110132656 | Horiguchi et al. | Jun 2011 | A1 |
20110143467 | Xiong et al. | Jun 2011 | A1 |
20110147760 | Ogihara et al. | Jun 2011 | A1 |
20110151602 | Speier | Jun 2011 | A1 |
20110159615 | Lai | Jun 2011 | A1 |
20110210357 | Kaiser et al. | Sep 2011 | A1 |
20110244611 | Kim | Oct 2011 | A1 |
20110291134 | Kang | Dec 2011 | A1 |
20110297914 | Zheng et al. | Dec 2011 | A1 |
20110312131 | Renavikar et al. | Dec 2011 | A1 |
20120018494 | Jang et al. | Jan 2012 | A1 |
20120064642 | Huang et al. | Mar 2012 | A1 |
20120134065 | Furuya et al. | May 2012 | A1 |
20130019996 | Routledge | Jan 2013 | A1 |
20130038416 | Arai et al. | Feb 2013 | A1 |
20130130440 | Hu et al. | May 2013 | A1 |
20130134591 | Sakamoto et al. | May 2013 | A1 |
20130161682 | Liang et al. | Jun 2013 | A1 |
20140071580 | Higginson et al. | Mar 2014 | A1 |
Number | Date | Country |
---|---|---|
1792128 | Jun 2006 | CN |
101164150 | Apr 2008 | CN |
101863035 | Oct 2010 | CN |
102393177 | Mar 2012 | CN |
10 2007 033000 | Jan 2009 | DE |
61-265218 | Nov 1986 | JP |
07-060675 | Mar 1995 | JP |
11-142878 | May 1999 | JP |
2001-298072 | Oct 2001 | JP |
2001-353682 | Dec 2001 | JP |
2002-134822 | May 2002 | JP |
2002-164695 | Jun 2002 | JP |
2002-176291 | Jun 2002 | JP |
2002-240943 | Aug 2002 | JP |
2004-095944 | Mar 2004 | JP |
2008-200821 | Sep 2008 | JP |
2010-056458 | Mar 2010 | JP |
2010-161212 | Jul 2010 | JP |
2010-186829 | Aug 2010 | JP |
2011-181834 | Sep 2011 | JP |
10-0610632 | Aug 2006 | KR |
10-2007-0042214 | Apr 2007 | KR |
10-2007-0093091 | Sep 2007 | KR |
10-0973928 | Aug 2010 | KR |
10-1001454 | Dec 2010 | KR |
10-2007-0006885 | Jan 2011 | KR |
10-2011-0084888 | Jul 2011 | KR |
WO 00-67543 | Nov 2000 | WO |
WO 2005-099310 | Oct 2005 | WO |
WO 2008-052594 | May 2008 | WO |
WO 2011123285 | Oct 2011 | WO |
WO 2014050586 | Apr 2014 | WO |
Entry |
---|
Asano, Kazutoshi, et al., “Fundamental Study of an Electrostatic Chuck for Silicon Wafer Handling” IEEE Transactions on Industry Applications, vol. 38, No. 3, May/Jun. 2002, pp. 840-845. |
Bower, C.A., et al., “Active-Matrix OLED Display Backplanes Using Transfer-Printed Microscale Integrated Circuits”, IEEE, 2010 Electronic Components and Technology Conference, pp. 1339-1343. |
“Characteristics of electrostatic Chuck(ESC)” Advanced Materials Research Group, New Technology Research Laboratory, 2000, pp. 51-53 accessed at http://www.socnb.com/report/ptech_e/2000p51_e.pdf. |
Guerre, Roland, et al, “Selective Transfer Technology for Microdevice Distribution” Journal of Microelectromechanical Systems, vol. 17, No. 1, Feb. 2008, pp. 157-165. |
Han, Min-Koo, “AM backplane for AMOLED” Proc. of ASID '06, 8-12, Oct, New Delhi, pp. 53-58. |
Harris, Jonathan H., “Sintered Aluminum Nitride Ceramics for High-Power Electronic Applications” Journal of the Minerals, Metals and Materials Society, vol. 50, No. 6, Jun. 1998, p. 56. |
Horwitz, Chris M., “Electrostatic Chucks: Frequently Asked Questions” Electrogrip, 2006, 10 pgs, accessed at www.electrogrip.com. |
Hossick-Schott, Joachim, “Prospects for the ultimate energy density of oxide-based capacitor anodes” Proceedings of CARTS Europe, Barcelona, Spain, 2007, 10 pgs. |
Lee, San Youl, et al., “Wafer-level fabrication of GAN-based vertical light-emitting diodes using a multi-functional bonding material system” Semicond. Sci. Technol. 24, 2009, 4 pgs. |
“Major Research Thrust: Epitaxial Layer Tranfer by Laser Lift-off” Purdue University, Heterogeneous Integration Research Group, accessed at https://engineering.purdue.edu/HetInt/project_epitaxial_layer_transfer_llo.htm, last updated Aug. 2003. |
Mei, Zequn, et al., “Low-Temperature Solders” Hewlett-Packard Journal, Article 10, Aug. 1996, pp. 1-10. |
Mercado, Lei, L., et al., “A Mechanical Approach to Overcome RF MEMS Switch Stiction Problem” 2003 Electronic Components and Technology Conference, pp. 377-384. |
Miskys, Claudio R., et al., “Freestanding GaN-substrates and devices” phys. Stat. sol. © 0, No. 6, 2003, pp. 1627-1650. |
“Principles of Electrostatic Chucks: 1—Techniques for High Performance Grip and Release” ElectroGrip, Principles1 rev3 May 2006, 2 pgs, accessed at www.electrogrip.com. |
Steigerwald, Daniel, et al., “III-V Nitride Semiconductors for High-Performance Blue and Green Light-Emitting Devices” article appears in journal JOM 49 (9) 1997, pp. 18-23. Article accessed Nov. 2, 2011 at http://www.tms.org/pubs/journals/jom/9709/setigerwald-9709.html, 12 pgs. |
Widas, Robert, “Electrostatic Substrate Clamping for Next Generation Semiconductor Devices” Apr. 21, 1999, 4 pgs. |
PCT International Search Report and Written Opinion for International Application No. PCT/US2014/016418, dated May 27, 2014, 10 pages. |
PCT International Search Report and Written Opinion for International Application No. PCT/US2015/032292, dated Sep. 23, 2015, 10 pages. |
Number | Date | Country | |
---|---|---|---|
20170182667 A1 | Jun 2017 | US |
Number | Date | Country | |
---|---|---|---|
Parent | 14303483 | Jun 2014 | US |
Child | 15460915 | US |