It is one object of the present invention to provide a semiconductor storage device and a manufacturing method thereof to solve the above-mentioned drawbacks or shortcomings of the prior art.

One aspect of the invention provides a semiconductor memory device including a substrate, a first dielectric layer on the substrate, a bottom electrode on the first dielectric layer, a second dielectric layer on the first dielectric layer, and a top electrode in the second dielectric layer. The top electrode comprises a lower portion around the bottom electrode and a tapered upper portion. A third dielectric layer is disposed above the bottom electrode and around the tapered upper portion of the top electrode. A resistive-switching layer is disposed between a sidewall of the bottom electrode and a sidewall of the lower portion of the top electrode and between the third dielectric layer and a sidewall of the tapered upper portion of the top electrode. An air gap is disposed in the third dielectric layer.

According to some embodiments, the semiconductor memory device further includes a dielectric block layer between the second dielectric layer and the first dielectric layer.

According to some embodiments, the top electrode is disposed on the dielectric block layer.

According to some embodiments, the resistive-switching layer includes NiO_x, Ta_yO_x, TiO_x, HfO_x, WO_x, ZrO_x, Al_yO_x, SrTiO_x, Nb_yO_x, or Y_yO_x, wherein x>0, y>0.

According to some embodiments, the top electrode includes TiN, TaN or Pt.

According to some embodiments, a top surface of the second dielectric layer is coplanar with a top surface of the top electrode.