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III-Nitride light-emitting diodes (LEDs) and laser diodes (LDs) are light sources covering ultraviolet (UV) and visible spectral regimes, which offer benefits including compact size, wavelength tuning, long lifetime, and sustainability. UV light sources have a range of applications in the fields of biology and medicine, such as sterilization and the purification of both water and air, where visible light emitters have been used in miniaturized photonic devices for optogenetic applications and other light-based therapies. Those III-Nitride light sources provide tremendous potential to be integrated with silicon (Si)-based lab-on-a-chip (LOC) technology, which typically requires the coupling of an external light source through fiber optic cable, limiting the field deployment of the devices. Integrating an on-chip III-Nitride light source with these devices opens the door to complete LOC technology, allowing for the simultaneous detection of multiple bio agents on a single platform without the need for external photonic sources. While most integrated microsystems still rely on wafer bonding at the device or wafer level, one promising method to achieve the integration of III-nitride UV and visible LEDs and LDs with conventional Si photonics and complementary metal-oxide-semiconductor (CMOS) platforms is through the use of micro-transfer printing (µTP). µTP has greater tolerances in alignment than techniques such as flip-chip integration and allows for the transfer of many devices at once. Additionally, the µTP process does not call for the complex and high temperature processing required for standard wafer bonding or necessitate complicated growth and lattice matching needed for monolithic integration. To enable µTP, an elastomeric, such as polydimethylsiloxane (PDMS), is utilized to create a transfer stamp that is employed for the precise selection of fabricated semiconductor devices for transfer from a source wafer to a target wafer. III-Nitride LEDs or LDs epitaxial structures are grown on a source wafer and fabricated through the creation of tethered coupons, or individual devices. This is accomplished by utilizing III-nitride materials grown on (111) Si. These devices can be fabricated through standard lithography and etching processes, etching down to the (111) Si substrate. A larger mesa can be patterned and etched into the Si substrate, exposing the sidewalls for wet chemical etching. The finished devices are then encapsulated in SiNxthrough plasma enhanced chemical vapor deposition (PECVD), which is patterned through standard lithography to define tethers and anchors for the subsequent wet etch. The fabricated devices are oriented in such a way as to take advantage of the difference in etch rates (>100x) of Si(110) and Si(111) in potassium hydroxide (KOH), where etching proceeds along the <110> direction. After KOH etching, the devices are left encapsulated in SiNxand suspended over the silicon substrate with an air gap, while the anchors and tethers are left largely unaffected.This enables the elastomer stamp to press down, breaking the tethers, and releasing the device. The stamp is then able to transfer the device to a target wafer that has been coated and patterned with InterVia, a spin-on dielectric material that acts as an adhesion layer. The stamp is pressed into the target wafer in such a way that the device is adhered to the target and released from the elastomer stamp. This technique can be applied to LEDs and LDs grown on (111) Si, allowing for the heterogeneous integration of III-nitride LED and LDs with conventional CMOS and Si photonic integrated circuits (PICs) as on-chip light sources, opening the door to complete LOC technology without the need for additional external photonic sources.
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Semi-Automated Soft Robotic Stamp Transfer Machine for Van Der Waals Heterostructure Device Assembly
Monolayer materials can be vertically stacked into artificial solids, known as the van der Waals heterostructures (vd-WHs) [1], to realize a new class of ultrathin optoelectronic, electronic, and quantum devices, which have significant potential to revolutionize the field of nanoelectronics and impact a wide range of application areas including transparent displays, sensor arrays, and logic and memory circuits. However, today’s assembly of vdWH devices is still primarily through manual manipulation, which lacks the precision and repeatability needed for the scalable manufacturing of wafer-scale vdWH device arrays outside a research setting. Aiming to enable the automated, scalable, and repeatable manufacturing of vdWH device arrays, this paper presents the design, prototyping, and preliminary tests of a novel semi-automated soft-robotic stamp transfer system for thin-film materials. The system uses a dry elastomer stamp with its adhesion controlled by temperature and peeling speed for material transfer. A combination of electromagnetic and pneumatic actuation is used for the soft-robotic stamp to realize a gentle and uniform pressing of the stamp over the material. An optical microscope, force sensors, and temperature sensors are integrated to enable instrumentation of the transfer process. Preliminary experiments were conducted using our system to conduct for exfoliated graphite transfer. Test results demonstrate the reliable and repeatable transfer of 2D crystal flakes, which show promise to enable the deterministic and scalable assembly of vdWH-based device arrays at wafer scale.
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- Award ID(s):
- 2243477
- PAR ID:
- 10501585
- Publisher / Repository:
- American Society of Mechanical Engineers
- Date Published:
- ISBN:
- 978-0-7918-8724-0
- Format(s):
- Medium: X
- Location:
- New Brunswick, New Jersey, USA
- Sponsoring Org:
- National Science Foundation
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