Fabrication of Porous Membranes for MEMS Packaging by One-Step Anodization in Sulfuric Acid

This paper reports a method for fast-release and safe-sealing of thin film encapsulation (TFE) for packaging of piezoelectric MEMS devices fabricated on cavity-SOI wafers. For fast releasing of the TFE, MEMS device trenches and the cavity below them were utilized and this combination acted as etch channels. Etchant can attack the sacrificial layer from the bottom of the MEMS device as well as side-located channels. A side-located etch channel scheme was chosen to ensure safe-sealing without mass-loading. 120 µm × 120 µm sized encapsulation on top of the MEMS device with eight isolation trenches connected to the cavity was released in 25 min. This is twice as fast as the TFE fabricated on bulk wafer using a similar encapsulation scheme. This reduction in release time is a consequence of a prefabricated cavity underneath the device which allows the etchant to attack the sacrificial layer at multiple locations as etchant can pass from one isolation trench to another.

Section: Introductionmentioning

confidence: 99%

Cavity-enhanced sacrificial layer micromachining for faster release of thin film encapsulated MEMS

Lee¹,

Sharma²,

Narducci³

et al. 2015

“…Due to its tunable porosity, its electrical insulation and its chemical resistance, PAA has been used in many applications such as; dyeing of aluminum layers [1], humidity sensors [8], microcantilevers [9], antireflection structures [10], photonics crystals [11], insulating layers for electronic devices [12,13] and hermetic packaging for microsystems [13][14][15]. Moreover, due to its capillaries, high aspect ratio structures of alumina were fabricated [9,16,17] and due to its nanometer-range porosity, PAA was employed, as a template or as a mask for the fabrication of nanostructured materials [18], nanotubes [19,20], nanowires [21,22], nanoholes [23] and nanodots [24].…”

Section: Introductionmentioning

confidence: 99%

Micro-patterning of porous alumina layers with aligned nanopores

Canonica

Wardle

Lozano

2014

“…However, this scheme has the drawback of a longer release time because the sacrificial layer material should be removed through a long etching path from the sidewall to the center of the TFE, as shown in figure 1(b) [9][10][11]. On the other hand, a porous cap layer with micro-or nano-etch holes may also be used to solve the above issues [12,13]. In these approaches, the nano-or micron-sized pores play the role of an etch channel, which helps in the fast removal of the sacrificial layer and safe sealing of the TFE without mass loading on the MEMS devices.…”

Section: Introductionmentioning

confidence: 99%

Development and evaluation of a two-level functional structure for the thin film encapsulation

Lee¹,

Sharma²,

Singh³

et al. 2013

This paper reports a two level capping structure for encapsulating micro-electro-mechanical system (MEMS) devices. The two level capping solves the main issue of the longer release time as well as safe sealing in thin film encapsulation (TFE). In this technique, the first cap layer has many etch holes, which were uniformly distributed on it to enhance the removal of the sacrificial layer. The second cap layer forms a cap on every etch hole in the first cap layer to protect the mass loading on MEMS devices. This technique was found to be very effective in reducing the release time of the TFE. For the 1200 µm × 1200 µm sized cavity encapsulation, this technique decreases the release time of the TFE by a factor of 24 in comparison to the sidewall located channel scheme. The presented technique also helps in reducing the size of TFE as the etch holes are uniformly distributed on the TFE itself. Wide seal rings were not required to accommodate sidewall channels.