For the application of a high-density, low-cost 3D vertical X-point array (V-XPA), we report the characteristics of the atomic layer deposition (ALD) available simple In-Te binary ovonic threshold switch (OTS) and its combination with an $\mathrm{HfO}_{\mathrm{x}}$ buffer layer. In-Te binary OTS exhibited a highly stable threshold voltage $(\mathrm{V}_{\mathrm{th}})$ and low delta firing voltage $(\Delta\mathrm{V}_{\mathrm{ff}}=\mathrm{V}_{\mathrm{ff}}-\mathrm{V}_{\mathrm{th}})$ with a low off-leakage current ($\mathrm{I}_{\text{off}}$) of several nanoamperes, which are the essential requirements for a mega-array. To reduce the high $\mathrm{I}_{\text{off}}$ of the V-XPA, which originates from the perimeter shape selector area, a sub-nanometer ultrathin $\mathrm{HfO}_{\mathrm{x}}$ buffer layer was successfully applied for the current confinement, yielding an excellent $\mathrm{I}_{\text{off}}$ of 1 nA when combined with the In-Te binary OTS.