Use of nanoporous columnar thin film in the wafer-level packaging of MEMS devices

Abstract

This paper presents a new packaging technology that uses a nanoporous columnar thin film to seal microelectromechanical system (MEMS) devices at the wafer level. In the proposed packaging process, the processing temperature is 350 • C. The process is relatively inexpensive compared to wafer level packaging processes, because the wafer-bonding step is eliminated and the die size is shrunk. In the suggested approach, a sputtered columnar thin film at room temperature forms vertical nanopores as etch holes, and an air cavity is formed by the removal of a sacrificial layer through the nanopores in the columnar membrane. Subsequent hermetic vacuum packaging of the cavity is achieved by depositing thin films over the membrane under low pressure. The hermeticity of the packaging was verified by using an optical surface morphology microscope to measure the deflection change of the sealing membrane before and after breaking of the vacuum through an interconnected membrane. The long-term hermeticity was monitored by measuring the maximum central deflection of the PECVD sealing layer over a period of 170 days. The precise pressure (0.7 Torr) and short-term (30 days) pressure change inside the cavity were measured by encapsulated Ni Pirani gauges, representing packaged freestanding MEMS devices.

Unconventional Use of a Photoresist as a Nitrogen Gas Generator Forming Transparent Dome‐Shaped Microcavities

“…Figure 1c shows the optical image of the final structure. [11,12] 2.2. Figure 1d to f represent scanning electron microscope (SEM) images inside the domeshaped structure (cross-sections near the center of the circular pattern).…”

“…It can be observed that the fabricated microcavities have clear dome shapes. [12,16] One possible application for which the proposed technique might be useful is in preparing a transparent MEMS package of encapsulated N 2 . In the case of line patterns with no junction points such as "I" and "S" patterns, the final structures show homogeneous, smooth shapes along the lines.…”

New selective two-step anodization of porous anodic alumina for thin-film encapsulation

“…To satisfy the market demand for MEMS devices, wafer-level packaging (WLP) has been widely developed by many research groups [2]. Among the WLP approaches in MEMS, thin-film encapsulation promises smaller area waste and lower cost [3,4].…”

“…To make matters worse, in the case of a micro-system with lateral etching holes, the process time for sacrificial layer etching is very long and depends on the lithography technology [6]. Also etching holes in the membrane can weaken the mechanical strength of the final system [2]. To avoid these problems, thin-film encapsulation with nano-porous material has been proposed.…”

A Wafer-Level Vacuum Package Using Glass-Reflowed Silicon Through-Wafer Interconnection for Nano/Micro Devices

“…The lateral feed-through establishes a metal line on the same surface of NMDS. [10][11][12][13][14] Therefore, the overall size of devices is larger than devices with the vertical feed-through. Furthermore, the fabrication process becomes complicated, which is unsuitable for batch processing.…”