SATPC0034297 Tab 04 4 SOW.pdf

Project Title: On-Demand Manufacturing and Radiation-Hardened Electronics of Microgravity- CVD 2D Semiconductors Principal Investigator: Yuxuan Cosmi Lin, Assistant Professor, Department of Materials Science and Engineering, Texas A&M University. E-mail: yxlin@tamu.edu Period of Performnce: March 1, 2024 – 30, 2024 Executive Summary The emerging 2D semiconductors have been envisioned as promising candidates for the next-generation post-silicon ultra-scaled transistor technology1, which, at the same time, are suitable for on-demand space manufacturing for high-performance radiation-hardened electronics. In this project, we propose to systematically investigate different radiation effects, including total ionizing dose (TID), single event effects (SEE) and displacement damage dose (DDD), on the atomic structures and electrical properties of 2D semiconductors. Resonance Raman spectroscopy, and advanced atomic force microscopy (AFM) such as conductive AFM (C-AFM), kelvin probe force microscopy (KPFM), and scanning capacitive microscopy (SCM) will be carried on to characterize the radiation-induced defect states and their local electrical characterization at the nanoscale. The microscopic characteristics will be correlated with the current-voltage (I-V) characteristics when 2D semiconductors are fabricated into field-effect transistors (FETs). Based on the investigation, we are going to develop fabrication processes and device technologies, and demonstrate high-performance, radiation-hardened integrated circuits made of 2D semiconductors.

Background and Motivation Space offers special manufacturing environments because of its near-vacuum state, microgravity, and higher levels of radiation2,3. Manufacturing technologies in different application domains have been proposed which can benefit from such a unique in-space platform. Meanwhile, these unique characteristics provide both opportunities and challenges for in-space manufacturing and other space applications. Researchers are actively looking for new materials and microelectronic technologies which can be manufactured and used in space simultaneously. 2D semiconductor technologies may be a promising candidate which can both benefit from the unique microgravity-manufacturing environment and fulfil the radiation hardiness requirements for in-space microelectronic applications. On one hand, the microgravity environment eliminates gravity-involved fluidic behaviors such as buoyancy, sedimentation, and convection, which would promote a quasi-static growth of high-quality, single-crystalline, and defect-free 2D semiconductor materials (such as MoS2). This has been a major development challenge for scaling up these emerging semiconductors for ultra-scaled transistor technologies in a terrestrial growth system1,4. On the other hand, because of its atomic-scale thickness (e.g., a monolayer MoS2 is only 0.7 nm), their capture cross-sections of ionizing radiations (such as X rays, gamma rays, high-energy electrons, protons, alpha particles and other heavy ions) are extremely small. As a result, transistors, memory devices and integrated circuits made with 2D semiconductors are naturally radiation hard and suitable for space applications5-7.

Preliminary investigations on low-dimensional semiconductors (such as 1D carbon nanotubes, 2D graphene MoS2, WS2, etc.) have shown promising trends on the radiation hard characteristics of these materials, allowing for their potential applications in radiation-hardened electronics6-8. However, some issues still remain, including the following: (i) the atomistic origins of the radiations effects and their correlations with the transistor characteristics are still to be investigated; (ii) the transistor architectures in the previous studies were not optimized for high performance, and were not designed specifically for radiation-hard applications; (iii) the radiation conditions used in the majority of the previous studies are incomparable with the testing standards for radiation-hard electronics.

Project Description In this project, the following tasks will be executed.

Task 1: Radiation experiments on microgravity-CVD 2D semiconductors. We are going to design and implement a series radiation experiments on monolayer MoS2 films synthesized by chemical vapor deposition (CVD) either in terrestrial or in microgravity environments. MoS2 films will be transferred onto both insulating substrates (such as sapphire) and back-gate substrates (such as 300 nm SiO2/Si substrates and 5 nm Al2O3/Si substrates) in order to differentiate the radiation effects on MoS2 itself from those on the gate dielectrics. Gamma ray and neutron radiation will be conducted at the TEES Nuclear Engineering & Science Center for the TID and DDD tests, while protons, alpha particle, and other heavy ion radiations will be conducted at the TAMU Cyclotron Institute for the SEE tests. A series of radiation conditions that are in compliance with the testing standards of radiation-hardened electronics will be employed to better understand the radiation effects on the material qualities and their electrical characterization.

Task 2: Atomistic and multimodal characterization of radiated 2D semiconductors. To characterize how the atomic structures evolve with different radiation conditions, a variety of advanced material characterization methods will be used, such as: (i) Resonance Raman spectroscopy to measure multiple second-order Raman scattering modes which are extremely sensitive to defects, impurities, and induced charges and strains; and (ii) advanced AFM modes, including C-AFM, KPFM, and SCM to capture the out-of-plane defect-associated conductance, surface potential, and trap capacitance at the nanoscale. These measurements will be performed on pristine MoS2 and radiated MoS2 (under different radiation conditions) on different substrates and correlated with the device characteristics (Task 3) to better understand the physical and chemical origins of various radiation effects.

Task 3: Radiation-hardened 2D semiconductor transistor technology development. Besides the semiconductor channel, other auxiliary structures such as the substrate, gate dielectrics, gate metal, and source-drain contacts also need to be tailored for radiation hard applications. Based on our previous development of high-performance and ultra-scaled MoS2 FETs, additional design constraint related to radiation hardening requirements will be taken into account. The key design considerations related to radiation tolerance include: (i) Insulating substrates such as sapphire should be used to mitigate the single event burnout (SEB) and single-event gate rupture (SEGR). (ii) The material selections and thicknesses of the gate dielectrics and metal electrodes should be fully optimized in terms of both the charge robustness and radiation capture cross-sections, in order to suppress the TID. (iii) In addition to the optimized transistor architectures, additional test structures such as hall bar structures, transfer length method (TLM) test structures, and metal-insulator-semiconductor (MIS) capacitance structures should also be implemented for the extraction and separation of impacts of different radiation effects on the key device metrics. This analysis should be coordinated with the atomic/nano-scale characterization results discussed in Task 2 to better understand the physical and chemical origins of the radiation-induced degradation on 2D semiconductors. As the initial effort in the interest of the proposed period, we are going to run TCAD simulations to verify and optimize the proposed design, and based on the simulation results, to develop an end-to-end fabrication and test flow framework to prepare for the next stage of the proposed work.

Timeline & Deliverables The proposed timeline is summarized in the following table:

Q1 (Mar.-May 2024) Q2 (Jun.-Aug. 2024) Q3 (Sep.-Nov. 2024) Task 1 Sample prep. Rad. exp. batch 1 Sample prep. Rad. exp. batch 2 Task 2 Resonance Raman Spectroscopy Advanced AFM (C-AFM, KPFM, SCM) Task 3 TCAD simulation Device fabrication & test develop.

The outcome of the project will be delivered through monthly tag-up meetings and quarterly reports. Below is a summary of the key milestones:

Kick-off brief (3/15/2024): all-hands kick-off meeting between the TAMU PI, researcher and NASA collaborators. Briefing about the project objectives, proposed approaches, and timelines.

Bimonthly report 1 (4/30/2024): protocol development for resonance Raman spectroscopy.

Bimonthly report 2 (6/28/2024): first batch of radiation experiments; radiation effects captured by resonance Raman spectroscopy; initial results on advanced AFM.

Bimonthly report 3 (8/30/2024): TCAD simulation results; radiation effects captured by advanced AFM;

protocol development of device fabrication.

Bimonthly report 4 (10/31/2024): second batch of radiation experiments; in-depth study on Resonance Raman, advanced AFM, and TEM; protocol development of device test.

Final report (11/22/2024): Final program review.

Reference

1 Cao, W. et al. The future transistors. Nature 620, 501-515 (2023).

2 Prater, T., Werkheiser, M. J., Ledbetter, F. & Morgan, K. in 2018 AIAA SPACE and Astronautics Forum and Exposition. 5364.

3 Bhundiya, H. G., Royer, F. & Cordero, Z. Engineering framework for assessing materials and processes for in-space manufacturing. Journal of Materials Engineering and Performance 31, 6045-6059 (2022).

4 Briggs, N. et al. A roadmap for electronic grade 2D materials. 2D Materials 6, 022001 (2019).

5 Fleetwood, D. Perspective on radiation effects in nanoscale metal–oxide–semiconductor devices.

Applied Physics Letters 121 (2022).

6 Arnold, A. J., Shi, T., Jovanovic, I. & Das, S. Extraordinary radiation hardness of atomically thin MoS2.

ACS applied materials & interfaces 11, 8391-8399 (2019).

7 Zhu, M. et al. Radiation-hardened and repairable integrated circuits based on carbon nanotube transistors with ion gel gates. Nature Electronics 3, 622-629 (2020).

8 Kim, T.-Y. et al. Irradiation effects of high-energy proton beams on MoS2 field effect transistors. ACS nano 8, 2774-2781 (2014).