(Invited) MoS 2 Thin Films for Piezoresistive Strain Sensors

• Published in: Meeting abstracts (Electrochemical Society) Vol. MA2025-01; no. 36; p. 1732
• Main Authors: Ono, Takahito, Zhu, Minjie, Suo, Joichiro, Inomata, Naoki
• Format: Journal Article
• Language: English
• Published: 11.07.2025
• ISSN: 2151-2043; 2151-2035
• DOI: 10.1149/MA2025-01361732mtgabs

Atomic layered molybdenum disulfide (MoS 2 ) is one of the most promising two-dimensional (2D) materials for next-generation microelectromechanical devices, including nanoelectromechanical sensors, flexible tactile sensors, and ultrasensitive miniaturized transducers (1). However, 2D MoS 2 -based sensors have not yet been put to practical use due to challenges in material synthesis for large areas and mass production of thin film fabrication technology. In this talk, we introduce the synthesis of the MoS 2 thin films and the doping effect. Firstly, 2D MoS 2 films were prepared using the general low-pressure chemical vapor deposition (LPCVD) method (2). As sources, MoO 3 powder and high-purity (99%) sulfur powder were used, and those source temperatures were controlled at 690-710 ºC and 135 ºC under Ar carrier gas in a furnace, respectively. A 2D polycrystalline film was deposited on an oxidized Si substrate. The high-quality continuous films were synthesized at a pressure of 372 Pa. Higher growth pressure leads to higher vapor pressure of MoO 3 , increasing particle-like MoS 2 nucleation. It was found from the observation of the E 1 2g vibration mode of the in-plane vibration of Mo and S atoms that the monolayered film was successfully obtained. In order to evaluate the piezoresistivity, the MoS 2 film was patterned, and electrodes were formed on the MoS 2 resistive elements. A four-point bending method was utilized to apply strain to the MoS 2 resistor. As a result, a gauge factor of ~104 was observed for the monolayered film, which is close to the gauge factor of an exfoliated MoS 2 monolayer film, indicating that a high-quality monolayer was formed. One of the issues with the mass production of MoS 2 films based on LPCVD is the narrow process windows of high-quality MoS 2 films. Thus, we developed the simpler method of thin MoS 2 film preparation using sputtering. In the first step, thin Mo/Vanadium(V)/Mo films were deposited by magnetron sputtering, and in the second step, sulfurization was performed in the sulfur vapor furnace at 750 ºC, as shown in Fig. 1 (3). As a result, V-doped MoS 2 films of a few nanometers thickness with 1T-incorporated 2H structure were synthesized. The doping concentration can be controlled by the sputtering film thickness of the V layer (Fig. 2). The V-doping can reduce the resistivity of the films, which is beneficial to the sensor applications. From the XPS evaluation, S deficiency, which causes the binding energy downshift of the Mo 3d peak, is observed. Piezoresistive elements for evaluation of the piezoresistive effect were prepared as well, as shown in Fig. 3. Observation of piezoresistivity shows the highest gauge factor of ~140 at the V concentration of 15 wt.% (Fig. 4). This two-step film synthesis provides good film uniformity and compatibility with microfabrication, and the doping enhances the piezoresistive performance. References (1) M. Zhu, X. Du, S. Liu, J. Li, Z. Wang, T. Ono, “A review of strain sensors based on two-dimensional molybdenum disulfide, J. Mater. Chem. C 9, 9083, (2021). (2) M. Zhu, K. Sakamoto, J. Li, N. Inomata, M. Toda, T. Ono, " Piezoresistive strain sensor based on monolayer molybdenum disulfide continuous film deposited by chemical vapor deposition", J. Micromech. Microeng. 29, 055002 (2019). (3) M. Zhu, J. Li, N. Inomata, M. Toda, and T. Ono, " Vanadium-doped molybdenum disulfide film-based strain sensors with high gauge factor ", Appl. Phys. Exp. 12, 015003 (2019) Figure 1