Antonio Jose Trindade

Nanoscale-accuracy transfer printing of ultra-thin AlInGaN light-emitting diodes onto mechanically flexible substrates

The transfer printing of 2 μm-thick aluminum indium gallium nitride (AlInGaN) micron-size light-emitting diodes with 150 nm (±14 nm) minimum spacing is reported. The thin AlInGaN structures were assembled onto mechanically flexible polyethyleneterephthalate/polydimethylsiloxane substrates in a representative 16 × 16 array format using a modified dip-pen nano-patterning system. Devices in the array were positioned using a pre-calculated set of coordinates to demonstrate an automated transfer printing process. Individual printed array elements showed blue emission centered at 486 nm with a forward-directed optical output power up to 80 μW (355 mW/cm2) when operated at a current density of 20 A/cm2.

Heterogeneous integration of gallium nitride light-emitting diodes on diamond and silica by transfer printing.

We report the transfer printing of blue-emitting micron-scale light-emitting diodes (micro-LEDs) onto fused silica and diamond substrates without the use of intermediary adhesion layers. A consistent Van der Waals bond was achieved via liquid capillary action, despite curvature of the LED membranes following release from their native silicon growth substrates. The excellence of diamond as a heat-spreader allowed the printed membrane LEDs to achieve optical power output density of 10 W/cm(2) when operated at a current density of 254 A/cm(2). This high-current-density operation enabled optical data transmission from the LEDs at 400 Mbit/s.

Transfer Printing of AlGaInAs/InP Etched Facet Lasers to Si Substrates

InP-etched facet ridge lasers emitting in the optical C-band are heterogeneously integrated on Si substrates by microtransfer printing for the first time. 500 μm × 60 μm laser coupons are fabricated with a highly dense pitch on the native InP substrate. The laser epitaxial structure contains a 1-μm-thick InGaAs sacrificial layer. A resist anchoring system is used to restrain the devices while they are released by selectively etching the InGaAs layer with FeCl3:H2O (1:2) at 8 °C. Efficient thermal sinking is achieved by evaporating Ti-Au on the Si target substrate and annealing the printed devices at 300 °C. This integration strategy is particularly relevant for lasers being butt coupled to polymer or silicon-on-insulator (SOI) waveguides.

Pressure activated interconnection of micro transfer printed components

Micro transfer printing and other forms of micro assembly deterministically produce heterogeneously integrated systems of miniaturized components on non-native substrates. Most micro assembled systems include electrical interconnections to the miniaturized components, typically accomplished by metal wires formed on the non-native substrate after the assembly operation. An alternative scheme establishing interconnections during the assembly operation is a cost-effective manufacturing method for producing heterogeneous microsystems, and facilitates the repair of integrated microsystems, such as displays, by ex post facto addition of components to correct defects after system-level tests. This letter describes pressure-concentrating conductor structures formed on silicon (1 0 0) wafers to establish connections to preexisting conductive traces on glass and plastic substrates during micro transfer printing with an elastomer stamp. The pressure concentrators penetrate a polymer layer to form the connection, and...

Miniaturized LEDs for flat-panel displays

Inorganic light emitting diodes (LEDs) serve as bright pixel-level emitters in displays, from indoor/outdoor video walls with pixel sizes ranging from one to thirty millimeters to micro displays with more than one thousand pixels per inch. Pixel sizes that fall between those ranges, roughly 50 to 500 microns, are some of the most commercially significant ones, including flat panel displays used in smart phones, tablets, and televisions. Flat panel displays that use inorganic LEDs as pixel level emitters (μILED displays) can offer levels of brightness, transparency, and functionality that are difficult to achieve with other flat panel technologies. Cost-effective production of μILED displays requires techniques for precisely arranging sparse arrays of extremely miniaturized devices on a panel substrate, such as transfer printing with an elastomer stamp. Here we present lab-scale demonstrations of transfer printed μILED displays and the processes used to make them. Demonstrations include passive matrix μILED displays that use conventional off-the shelf drive ASICs and active matrix μILED displays that use miniaturized pixel-level control circuits from CMOS wafers. We present a discussion of key considerations in the design and fabrication of highly miniaturized emitters for μILED displays.

Heterogeneous Integration of Microscale Gallium Nitride Transistors by Micro-Transfer-Printing

Discrete gallium nitride high electron mobility transistors (HEMTs) are fabricated on oriented silicon, then undercut and assembled onto non-native silicon CMOS wafers by elastomer stamp micro-transfer-printing. The thin, less than 5 μm thick, gallium nitride transistors were then electrically interconnected using conventional thin-film metallization processes. Electrical measurements reveal that the heterogeneous integration process is benign to the underlying silicon transistors, and that the heterogeneous wide bandgap GaN transistors maintain their characteristic high voltage performance after being undercut and transferred to the non-native CMOS wafer.

Transfer-printing-based integration of a III-V-on-silicon distributed feedback laser

An electrically pumped DFB laser integrated on and coupled to a silicon waveguide circuit is demonstrated by transfer printing a 40 × 970 μm2 III-V coupon, defined on a III-V epitaxial wafer. A second-order grating defined in the silicon device layer with a period of 477 nm and a duty cycle of 75% was used for realizing single mode emission, while an adiabatic taper structure is used for coupling to the silicon waveguide layer. 18 mA threshold current and a maximum single-sided waveguide-coupled output power above 2 mW is obtained at 20°C. Single mode operation around 1550 nm with > 40 dB side mode suppression ratio (SMSR) is realized. This new integration approach allows for the very efficient use of the III-V material and the massively parallel integration of these coupons on a silicon photonic integrated circuit wafer. It also allows for the intimate integration of III-V opto-electronic components based on different epitaxial layer structures.

Miniature Heterogeneous Fan-Out Packages for High-Performance, Large-Format Systems

High-throughput assembly of miniature wafer-fabricated packages onto panel substrates provides a manufacturing framework for high-performance multi-functional displays and other large-format systems. Control circuits, light emitters, sensors, and other micro-components formed in high-density arrays on wafers use a variety of processes and materials that do not easily translate to large-format panel processing. Systems assembled from some or all of those components can therefore exhibit combinations of properties and performance characteristics that are difficult to achieve by panel processes only. Here, we demonstrate hierarchical assembly strategies for fabricating high-performance systems using elastomer stamp micro-transfer-printing. In this work, red, green and blue microscale inorganic LEDs (µILEDs) are fabricated on their respective native wafer substrates and then assembled onto non-native intermediate silicon wafers. The intermediate silicon wafer, populated with heterogeneous µILEDs, then undergoes conventional wafer-level processes, such a dielectric depositions and thin-film metallization, to form miniature fan-out packages. Here, we will demonstrate three heterogeneous µILEDs integrated within a 75 µm × 35 µm fan-out package. We will present how this microscale package can be undercut and then micro-transfer-printed directly onto large-format application substrates. The print-compatible packages also include sharp pressure-concentrating conductor structures which allow the heterogeneous fan-out packages to be electrically interconnected to large-format substrates during the printing operation. We will present functional µILED displays that have been fabricated using these assembly techniques. We will report on the benefits of using intermediate packaging substrates for manufacturing of high-performance large-format systems, such as displays. We will also demonstrate strategies for repairing large multi-functional systems.

Silicon photonics fiber-to-the-home transceiver array based on transfer-printing-based integration of III-V photodetectors

A 4-channel silicon photonics transceiver array for Point-to-Point (P2P) fiber-to-the-home (FTTH) optical networks at the central office (CO) side is demonstrated. A III-V O-band photodetector array was integrated onto the silicon photonic transmitter through transfer printing technology, showing a polarization-independent responsivity of 0.39 - 0.49 A/W in the O-band. The integrated PDs (30 × 40 μm2 mesa) have a 3 dB bandwidth of 11.5 GHz at -3 V bias. Together with high-speed C-band silicon ring modulators whose bandwidth is up to 15 GHz, operation of the transceiver array at 10 Gbit/s is demonstrated. The use of transfer printing for the integration of the III-V photodetectors allows for an efficient use of III-V material and enables the scalable integration of III-V devices on silicon photonics wafers, thereby reducing their cost.

Comparison of InGaAs and InAlAs sacrificial layers for release of InP-based devices

Heterogeneous integration of InP devices to Si substrates by adhesive-less micro transfer printing requires flat surfaces for optimum attachment and thermal sinking. InGaAs and InAlAs sacrificial layers are compared for the selective undercut of InP coupons by FeCl3:H2O (1:2). InAlAs offers isotropic etches and superior selectivity (> 4,000) to InP when compared with InGaAs. A 500 nm thick InAlAs sacrificial layer allows the release of wide coupons with a surface roughness < 2 nm and a flatness < 20 nm. The InAlAs release technology is applied to the transfer printing of a pre-fabricated InP laser to a Si substrate.