Probability to be positive for the membrane model in dimensions 2 and 3

We consider the membrane model on a box $V_N\subset {\mathbb{Z}}^n$ of size $(2N+1{)}^n$ with zero boundary condition in the subcritical dimensions $n=2$ and $n=3$. We show optimal estimates for the probability that the field is positive in a subset $D_N$ of $V_N$. In particular we obtain for $D_N=V_N$ that the probability to be positive on the entire domain is exponentially small and the rate is of the order of the surface area $N^{n-1}$.