Long-wave infrared detection technology holds core application value in military, medical, and industrial security fields. Its detection band aligns well with the thermal radiation peak of room-temperature objects, making it key to achieving uncooled thermal imaging. Currently, vanadium oxide and amorphous silicon, with their excellent temperature coefficient of resistance and tunable resistivity, have become the mainstream thermosensitive materials for uncooled infrared focal plane arrays. However, the research community continues to seek higher-performance alternatives. Palladium diselenide (PdSe₂), as an emerging two-dimensional semiconductor with layer‑tunable bandgap, excellent chemical stability, and good compatibility with low‑power CMOS back‑end‑of‑line processes, is regarded as an ideal platform for developing next‑generation high‑performance, low‑cost infrared detectors.

Despite the great potential of palladium diselenide, its practical application still faces severe performance trade‑off challenges. Ultrathin PdSe₂ films, though possessing a high temperature coefficient of resistance (TCR), are highly susceptible to ambient gas adsorption, while increasing the thickness improves stability but causes a rapid decrease in TCR, limiting the thermal sensitivity of the device. Furthermore, although introducing structures such as gold nanoparticles can enhance infrared absorption through photothermal effects, traditional physical processing is costly and chemical methods tend to introduce surface contamination. Therefore, how to break through the contradiction between thickness and sensitivity while maintaining material integrity and achieve scalable fabrication has become a technological bottleneck in this field, and this is the core motivation for research on optimizing the photothermoelectric performance of two‑dimensional materials through in‑situ modification strategies.

To address the above issues, a team from the University of Electronic Science and Technology of China and other institutions conducted systematic research using ZEPTOOLS' DMD maskless aligner. By developing an in-situ gold nanoparticle modification strategy combined with magnetron co‑sputtering and low‑temperature selenization processes, the team successfully overcame the inherent trade‑off challenge in the infrared detection performance of ultrathin palladium diselenide films.

Title: In Situ Au Nanoparticle Decorated Multilayer PdSe2 Films for Enhanced Bolometric Photodetection
Journal: ACS Applied Materials & Interfaces
URL：https://doi.org/10.1021/acsami.6c02930

To address the performance trade‑off challenge of two‑dimensional palladium diselenide (PdSe₂) films in infrared detection, this study proposes a scalable, high‑performance strategy. The researchers deposited Au‑Pd alloy precursor films on SiO₂ substrates via magnetron co‑sputtering, followed by a low‑temperature thermal selenization process at 300 °C. This induced a reaction‑enhanced phase transformation, resulting in the in‑situ growth of uniformly distributed Au nanoparticles within the multilayered PdSe₂ films. This in‑situ modification strategy not only effectively controls the doping concentration of Au particles but also avoids the high cost of conventional physical patterning and the potential surface contamination from chemical solution methods. It establishes the material foundation for obtaining ultrathin thermosensitive films of less than 15 nm with high chemical stability.

In the process of fabricating high‑performance infrared detectors, the precision of patterning directly determines the uniformity and response quality of the detection pixels. During the preparation of SiNₓ suspended membranes for infrared absorption measurement and subsequent complex array processing, the research team precisely used the ZEPTOOLS DMD maskless aligner for circuit definition and window opening. Through highly flexible digital exposure, this instrument sequentially completed channel definition of the Au‑nanoparticle‑decorated films, row electrode patterning, and aligned processing of multilayer insulating dielectrics on the Si wafer, ensuring the structural integrity of the devices at the micrometer scale. Benefiting from the patterning support provided by the DMD maskless aligner, the entire process flow could be strictly limited to below 300 °C, demonstrating the high compatibility of this technical route with the back‑end‑of‑line (BEOL) process of standard CMOS technology.

Through electrical characterization of thin films with different Au doping concentrations, the study found that the temperature coefficient of resistance (TCR) exhibits a non‑monotonic variation and reached an optimal value of −2.28 % K⁻¹ at an Au concentration of 11 at%. This phenomenon can be explained by a competition model between grain boundary engineering and Coulomb screening effects. An appropriate amount of Au nanoparticles acts as a nucleation inhibitor during selenization, significantly reducing the grain size of PdSe₂. The increased grain boundary density enhances carrier scattering, thereby raising the effective Schottky barrier height. However, when the concentration of Au nanoparticles becomes too high and they approach each other, the conductive nature of Au introduces a pronounced electrostatic screening effect, which reduces the barrier height at the grain boundaries and consequently causes the TCR to decrease again.

Based on the optimized material system, the research team successfully fabricated infrared detectors with high thermal resolution, achieving a temperature resolution as high as 11.8 mK, demonstrating excellent thermal sensitivity. Under infrared irradiation at a wavelength of 9.3 μm, the device with 34 at% Au doping achieved a high responsivity of 2.9 A/W and a detectivity of 5.1 × 10⁸ Jones, significantly outperforming the undoped pristine films. Finally, using an integrated 8 × 8 pixel focal plane array, the team successfully captured high‑fidelity thermographic images under room‑temperature, uncooled conditions. This not only validates the great potential of Au‑nanoparticle‑decorated PdSe₂ thin films for long‑wave infrared detection but also provides technical support for the development of next‑generation low‑cost, integrated thermal imaging systems.

The ZEPTOOLS ZML series is a DMD‑based maskless aligner that uses a DMD to replace traditional photomasks. It enables rapid and flexible design of lithographic patterns, supports 2D and 8‑bit grayscale lithography, and can meet arbitrary micron‑scale lithography requirements. It is widely used in many fields such as MEMS and microfluidics.