A display device for displaying articles of merchandise, such as books and posters, is provided. The device includes The device includes a strain-relaxed buffer stack over a substrate, a first fin structure disposed over the SRB stack and a liner layer extending along the portion of the second SRB layer and the first semiconductor material layer of the first fin structure. Therefore, the hindrance to the rotation of the planetary gears, when the planetary gears catch a foreign matter, can be prevented. The rigid filter includes a layer of microporous membrane having a plurality of pores and secured to the layer of rigid sintered polymer.