Ceramics for Microelectromechanical Systems Applications: A Review

Abstract

A comprehensive review of the application of different ceramics for MEMS devices is presented. Main ceramics materials used for MEMS systems and devices including alumina, zirconia, aluminum Nitride, Silicon Nitride, and LTCC are introduced. Conventional and new methods of fabricating each material are explained based on the literature, along with the advantages of the new approaches, mainly additive manufacturing, i.e., 3D-printing technologies. Various manufacturing processes with relevant sub-techniques are detailed and the ones that are more suitable to have an application for MEMS devices are highlighted with their properties. In the main body of this paper, each material with its application for MEMS is categorized and explained. The majority of works are within three main classifications, including the following: (i) using ceramics as a substrate for MEMS devices to be mounted or fabricated on top of it; (ii) ceramics are a part of the materials used for an MEMS device or a monolithic fabrication of MEMS and ceramics; and finally, (iii) using ceramics as packaging solution for MEMS devices. We elaborate on how ceramics may be superior substitutes over other materials when delicate MEMS-based systems need to be assembled or packaged by a simpler fabrication process as well as their advantages when they need to operate in harsh environments.

Keywords: 3D printing; MEMS; additive manufacturing; ceramics; microfabrication.

Figure 1

Conventional manufacturing of ceramics from beginning to final product [55].

Figure 2

Different types of additive manufacturing and their techniques based on ISO classification [56,57].

Figure 3

AM approaches for Si₃N₄ manufacturing: (A) SLS/SLM; (B) SLA; (C) LIS; (D) DLP, LCD; (E) DIW; (F) FDM; (G) BJ; (H) 3D printing (3DP); (I) LOM [63].

Figure 4

Five different 3D-printing techniques: Digital Light Processing (DLP), material jetting (MJ), Stereolithography (SLA), Fused Deposition Modeling (FDM), Direct Ink Writing (DIW) [64].

Figure 5

Microstructure of (a) monolithic (b) multi-structure of fabrication [66].

Figure 6

Shrinkage rate of the sintered ceramic with different sintering materials content, (a) (TiO₂) on top, (b) (CaCO₃) on left and (c) (MgO) on right in all direction (X direction in black, Y direction in red and Z direction in blue), direct lines indicate the shrinkage before adding materials [67].

Figure 7

DLP technique for AlN 3D manufacturing [69].

Figure 8

Laser power and velocity variation effect on surface morphology of zirconia sample [76].

Figure 9

Preheat temperature effect on sample cracks [76].

Figure 10

LTCC substrate and surface metallization by MJ technique [80].

Figure 11

Machine for (a) flat and (b) curve printing of LTCC [80].

Figure 12

Microstrip patch antenna and RF measurements including S11, VSWR, and gain. (a) 3D perspective of the circuit (b) fabricated circuit (c) S11 simulation and measurement (d) VSWR simulation (e) gain and efficiency (f) 3D radiation [80].

Figure 13

Fabricated curve LTCC with metallization on top by MJ technique. (a) fabricated curved LTCC (b) schematic diagram of the curved surface (c) shrinkage circuit after sintering with side views [80].

Figure 14

LTCC powder-preparation steps [81].

Figure 15

LTCC slurry and tape preparation [81].

Figure 16

(a–i) Fabrication process of Pt film, (j) overall view of the sensor, (k) zoomed view of the sensitive area. Performance of the sensor on the right (resistance variation vs. temperature) [91].

Figure 17

Fabrication process of AR lens (a) fabrication steps of AR lens, (b) polished surface of the curved aluminum (c) nanoporous alumina on curved aluminum (d) final optical image of the lens (left), AR lens vs. normal one comparison (top right), (a) AR lens on a yellow light, (b) nanopillars created by anodization of aluminum (bottom right) [95].

Figure 18

Alumina membrane gas sensor fabrication process (left), gas sensor under test in different temperatures (a–c) Si₃N₄ and (d–f) Al₂O₃ μHP (right) [98].

Figure 19

Fabricated bridge sealed with Alumina and silicon nitride (left). Measured S-parameters (right) [99].

Figure 20

Fabricated alumina nanopores with high aspect ratio (a) Two-step anodization process. (b) Cu seed layer deposition process. (c) Photoresist spin coating process. (d) Photolithography and patterning processes. (e) Cu electroplating process. (f) Removal of photoresist. (g) Etching of cu seed layer. (h) Etching of AAO membrane (left). Thin film packaging using glow discharge (center) and fabricated view from top illustrating anode and cathode metals (a) top view (b) SEM image (right) [100,101].

Figure 21

Flip-chip assembly on zirconia-silicate [103].

Figure 22

Fabricated flexible solar cell [104].

Figure 23

Fabrication process of micro-thruster [105].

Figure 24

Ammonia sensor and readout circuit (left), fabricated circuit (center), measured results of the sensor (right) [106].

Figure 25

Polishing machine (left), gaps found on the surface of AlN after polishing (right) [108].

Figure 26

(a)A PMUT device top view (b) cross section with different layers including AlN piezo layer [112].

Figure 27

Different type of PMUT devices in arrays, (a) top view of a PMUT device, (b) arrays of PMUTs 3Ddesign, (c) top view of arrays of PMUTs, (d) dimensions of PMUT arrays as a MEMS chip on CMOS device [112].

Figure 28

(a) A 3D view of AlN lamb wave resonator, (b) cross-section of AlN BAW resonator, (c) cross section of resonator with centered anchor, (d) cross section of a conventional lamb wave resonator [112].

Figure 29

SEM image of the fabricated optical 3 × 1 switch with zoom views and dimensions, (a) fabricated device top view; (b) mechanical stopper gap; (c) switching actuator gap; (d) air gap of the gap closing actuator; (e) air gap closing interface; and (f) etch profile of the optical stack. [129].

Figure 30

Silicon Nitride sealing fabrication process [130].

Figure 31

LTCC layers with embedded vias, cavities, and metallization as active substrate: (left) polished surface with vias on top, (right) active component and MEMS devices on top after final monolithic fabrication [134].

Figure 32

Fabricated capacitive MEMS switch with LTCC MEMS monolithic process, (a) Top image of the fabricated switch, (b) enlarged view (c) SEM image (left) LTCC-MEMS process flow (right) [134].

Figure 33

Cavities and via holes acting as a fluidic system for sensing application with embedded sensor [139].

Figure 34

Fabricated cantilever with LTCC ceramic materials (left) LTCC hotplate (right) [139].

Figure 35

LTCC humidity sensors made of different LTCC ceramic materials [139].