Micro/nanomechanical characterization of ceramic films for microdevices
Introduction
The advances in silicon process technology over the last three decades have led to the development of microcomponents known as microelectromechanical systems or MEMS. Researchers have fabricated a wide variety of sensors, actuators, valves, gear trains, turbines, nozzles and pumps (for a collection of works see Ref. [1]) with dimensions in the range of a couple to a few hundred micrometers. In MEMS devices, various forces associated with the devices scale down with the size. When the length of the machine decreases from 1 mm to 1 μm, the area decreases by a factor of a million and the volume decreases by a factor of a billion. The resistive forces such as friction, viscous drag and surface tension that are proportional to the area increase a thousand times more than the forces proportional to the volume such as inertial and electromagnetic forces. These forces lead to tribological concerns, which become critical because friction/stiction (static friction), wear and surface contamination affect device performance and in some cases can even prevent devices from working.
Although silicon based MEMS devices find such wide uses today, they lack high temperature capabilities with respect to both mechanical and electrical properties. Recently, researchers have been pursuing SiC as material for high-temperature microsensor and microactuator applications [2]. The high-temperature capability of SiC combined with its excellent mechanical properties, thermal dissipative characteristics, chemical inertness and optical transparency makes SiC an ideal choice for complementing polysilicon (polysilicon melts at 1400°C) in MEMS devices. Since MEMS devices need to be of low cost to be viable in most applications, researchers have found low-cost techniques of producing single-crystal 3C-SiC (cubic or β-SiC) films via epitaxial growth on large-area silicon substrates [3]. This technique allows high-volume batch processing and has the advantage of having silicon as the substrate, an inexpensive material for which microfabrication and micromachining technologies are well established. It is believed that these films will be well suited for MEMS devices.
Micro/nanomechanical and tribological characterization of these SiC films and their comparison to the polysilicon materials and films currently used in such small-scale devices is of critical importance. This paper presents the results of these studies conducted for the first time on 3C-SiC films as well as on the most commonly used materials in MEMS technology today: undoped single-crystal silicon and polysilicon films (undoped and doped).
Section snippets
Mechanical and tribological characterization
Hardness and elastic modulus were calculated from the load-displacement data obtained by nanoindentation using a Berkovich indenter on each sample at six different indentation loads ranging from 0.2 to 15 mN. In microscratch studies, a conical indenter having a tip radius of 1 μm and an included angle of 60°, was drawn over the sample surface, and the load was ramped up, until substantial damage occurred. The coefficient of friction was monitored during scratching. In order to obtain scratch
Hardness and elastic modulus
Representative load–displacement plots of indentations made at 15 mN peak indentation load on the undoped Si(100), undoped polysilicon film, doped polysilicon film, and SiC film are shown in Fig. 1. The SiC film exhibits the lowest indentation depth and highest slope of unloading curve, as compared to other samples, and the indentation depths and slopes of unloading curve for the undoped Si(100) are comparable to those of the undoped polysilicon and doped polysilicon films. The undoped Si(100),
Conclusions
The SiC film shows higher hardness, elastic modulus and scratch resistance as well as lower friction compared to the other materials currently used in MEMS devices. The fracture toughness of the SiC film is comparable to that of the undoped Si(100). In addition, the availability of a low-cost technique of producing the SiC film makes it an exceptional choice as a material for high-temperature MEMS applications.
Acknowledgements
The authors would like to thank Dr C. A. Zorman and Professor M. Mehregany of Case Western Reserve University for providing polysilicon and SiC films and for technical assistance. Financial support for this study was provided by the Office of Naval Research, Department of the Navy (Contract No. N00014-96-1-10292). The information herein does not necessarily reflect the position or policy of the government and no official endorsement should be inferred.
References (8)
- et al.
Wear
(1995) - et al.
Thin Solid Films
(1995) - W.S. Trimmer (Ed.), Micromachines and MEMS, Classic and Seminal Papers to 1990, IEEE Press, New York,...
- et al.
Appl. Phys. Lett.
(1992)
Cited by (114)
Experimental characterization and phase-field modeling of anisotropic brittle fracture in silicon
2023, Engineering Fracture MechanicsUnderstanding the role of surface mechanical properties in SiC surface machining
2023, Materials Science in Semiconductor ProcessingIn-situ study on compressive behaviors of different types of 3D SiC/SiC composites using X-ray computed tomography and digital image correlation
2023, Journal of Materials Research and TechnologyDetermination of polysilicon Weibull parameters from indentation fracture
2017, Thin Solid FilmsCitation Excerpt :A minimum of 20 indents were performed for indentation load ranging between 10 mN and 350 mN at room temperature in load controlled mode. Below 50 mN, there was no indentation cracking observed and the indentation depth was observed to be less than one third of the film thickness, as per Ref. [7], only for indentation loads ranging between 50 and 100 mN. An image using a scanning electron microscope (SEM) of a typical indent at 50 mN indent load and the corresponding load-displacement response is shown in Fig. 1.
Synthesis and characterization of monolithic CVD-SiC tubes
2016, Journal of the European Ceramic SocietyCitation Excerpt :The E values decrease linearly with fSi. The regression line obtained (with a coefficient of determination R2 equal to 0.89) evidences that E obeys a simple “parallel” rule of mixtures:E = fSi ESi + (1 – fSi)ESiC = (ESi − ESiC)fSi + ESiCwhere ESiC and ESi are the Young’s modulus of SiC and Si respectively, i.e., ESiC ≈ 400 GPa and ESi ≈ 130 GPa, in reasonably good agreement with values from the literature [27–29]. The macroscopic mechanical properties obtained from C-ring tests (Young’s modulus E and failure stress σ and strain ε) for each tube should be considered as apparent structural properties (Table 1).
Mechanical properties of computationally designed novel carbon enriched Si<inf>1-</inf><inf>x</inf>C<inf>x</inf> ceramics: A molecular dynamics simulation study
2015, Computational Materials ScienceCitation Excerpt :Silicon Carbide (SiC) is an important structural material with excellent wear and corrosion resistance [1–3], high hardness and strengths [4], high temperature and electrical stability [5,6] and many other useful properties.