Researchers from Huazhong University of Science and Technology have reported a self-aligned laser transfer (SALT) based on directional photothermal regulation strategies that enables high-precision, programmable transfer of microchips without the need of precise laser-to-die alignment.
Schematic illustration of the stamp with TCGC: (i) Schematic of the self-aligned mechanism of TCGC. (ii) Conversion of an asymmetric light intensity input to an even heat output by TCGC. (iii) Composition of TCGC: the upper layer is graphene with ordered atomic arrangement and high phonon transport efficiency; the lower layer is amorphous carbon with disordered atomic structure and low phonon transport efficiency. (iv) Schematic of thermal homogenization by light absorption and directional heat conduction through TCGC. Image from: Light: Science & Applications
The key innovation lies in the introduction of a special photothermal conversion material - thermal conductivity gradient carbon (TCGC). The TCGC can be prepared using a UV excimer laser to induce confined, self-limited carbonization of polyimide (PI), which naturally creates a gradient distribution of graphitization degree, with graphene (Gr) layer at the top and amorphous carbon (AC) layer at the bottom.
The unique gradient structure facilitates anisotropic and non-uniform spatial thermal conductivity distribution, thereby controlling the intensity of heat conduction in different directions.
Systematically experimental and numerical studies have showed the self-aligned mechanism, wherein the TCGC enables simultaneous laser absorption and directional heat conduction to non-ideal irradiated regions under non-uniform/misaligned infrared laser irradiation.
This efficient thermal homogenization ensures the synchronous release of a chip across all adhesive positions on the stamp, thereby mitigating the impact of irradiation deviations on the chip transfer path.
Additionally, the periodically arranged, grayscale-controlled TCGC can selectively release microchips without pre-planned scanning paths, offering distinct advantages in chip throughput for batch selective transfer and high-tolerance to irradiation deviation in the densely arranged chip arrays.
The SALT approach has enabled the heterogeneous integration and selective transfer of diverse micro-objects with varying shapes, sizes, and patterns onto various challenging surfaces, demonstrating reversible adhesion switchability of ~650, rapid response time ( ~ 30 ms), excellent size compatibility (from 100 μm to 1 mm), and high tolerance for irradiation deviations (transfer accuracy < 5 μm under a 30% beam offset).
Moreover, the successful integration of microchips onto three-dimensional substrates demonstrates the potential of SALT for advancing curved electronics.
Demonstrations involving multiple transfer printings of RGB MicroLED chips from different donor wafers highlight SALT’s self-aligned and batch-selective capabilities, which are crucial for efficient full-color MicroLED display assembly.
