Post-doping plasma for DRAM capacitors

Researchers from Ulsan National Institute of Science and Technology (UNIST), Pohang University of Science and Technology (POSTECH), and Seoul National University of Science and Technology developed a post-doping plasma (PDP) process to improve the performance of DRAM capacitors.

Aluminum-doped titanium dioxide (Al-doped TiO2) is a promising material for the DRAM capacitor’s dielectric layer due to its high dielectric constant and excellent leakage suppression, but conventional atomic layer deposition (ALD) fabrication methods can cause lattice disorder and oxygen vacancies, leading to material instability and increased leakage currents.

To overcome this, the PDP process involves first depositing the TiO2 dielectric layer via ALD and subsequently coating it with an ultrathin aluminum oxide layer, then exposing the film to a plasma composed of argon and oxygen. The plasma treatment transfers energy to the film’s surface, facilitating atomic-scale migration of aluminum dopants and reordering of the crystal lattice while simultaneously filling oxygen vacancies.

The team found that DRAM capacitors treated with the PDP process exhibited approximately 30% higher dielectric constants and up to nearly 40 times lower leakage currents. The approach has possibilities beyond DRAM, too, said Jihwan An, a professor at POSTECH, in a statement. “The atomic-layer process developed in this study can be applied broadly—not only to DRAM but also to next-generation electronic devices and energy storage systems.” [1]

Superconducting germanium

Researchers at New York University and University of Queensland produced a superconducting form of germanium.

The team used molecular beam epitaxy to dope the germanium with high levels of gallium while retaining the stability of its crystal structure. “Rather than ion implantation, molecular beam epitaxy was used to precisely incorporate gallium atoms into the germanium’s crystal lattice,” said Julian Steele, a physicist at the University of Queensland, in a press release. “Using epitaxy—growing thin crystal layers—means we can finally achieve the structural precision needed to understand and control how superconductivity emerges in these materials.”

The doped germanium was able to conduct electricity with zero resistance at 3.5 Kelvin. “These materials could underpin future quantum circuits, sensors, and low-power cryogenic electronics, all of which need clean interfaces between superconducting and semiconducting regions,” said Peter Jacobson, a physicist at the University of Queensland, in a press release. “Germanium is already a workhorse material for advanced semiconductor technologies, so by showing it can also become superconducting under controlled growth conditions there’s now potential for scalable, foundry-ready quantum devices.” [2]

Making n-type polymer semiconductors

Researchers from Pohang University of Science and Technology (POSTECH) and Sungkyunkwan University found that adjusting the concentration of a single dopant enables flexible organic polymer semiconductors to switch from p-type to n-type.

Most conjugated polymers naturally exhibit p-type behavior, but for practical applications, a single polymer system should exhibit both p-type and n-type characteristics to eliminate the need for separate materials or complex multilayer device architectures.

By doping a typically p-type polymer with a sufficiently high concentration of gold(III) chloride (AuCl3), the dominant charge carriers shift from holes to electrons. In investigating the underlying behavior, the team found that the oxidation states of gold and chloride ions evolve during doping, leading to a substitutional chlorination reaction with the polymer chains that induces structural reordering of the polymer backbone, realigning the molecular structure and reorganizing charge transport pathways.

The researchers used the approach to fabricate a p–n organic homojunction diode using a single polymer doped at two different concentrations that exhibited a rectification ratio tens of thousands of times greater than conventional single-material organic diodes. They noted that the approach shows potential to enable high-performance, flexible electronic devices with simplified architectures. [3]

References

[1] G. Lee, Y. Sunwoo, H. J. Kim, et al. In-situ post-doping plasma process during atomic layer deposition of Al-doped TiO2 for sub-nanometer lattice ordering and defect annihilation. Int. J. Extrem. Manuf. 8 015101 https://dx.doi.org/10.1088/2631-7990/ae037b

[2] J.A. Steele, P.J. Strohbeen, C. Verdi, et al. Superconductivity in substitutional Ga-hyperdoped Ge epitaxial thin films. Nat. Nanotechnol. (2025). https://doi.org/10.1038/s41565-025-02042-8

[3] E. Ok, S. Chung, S. H. Kim, et al. Accompanying Structural Transformations in Polarity Switching of Heavily Doped Conjugated Polymers. Adv. Mater. 37, no. 39 (2025): 37, 2505945. https://doi.org/10.1002/adma.202505945

Jesse Allen

(all posts) Jesse Allen is the Knowledge Center administrator and a senior editor at Semiconductor Engineering.