  \begin{tikzpicture}[scale=1.4,domain=0:2,>=latex]
    % horizontal axis
    \draw[->] (-0.2,0) -- (2.5,0) node[right] {$t/\tau$};
    \foreach \ta in {1,...,2} \draw (\ta cm,0) -- (\ta cm,-0.15) node[below] {\ta};
    \foreach \tb in {0.2,0.4,...,1.8} \draw (\tb cm,0) -- (\tb cm,-0.1);
    % vertical axis
    \draw[->] (0,-0.2) -- (0,1.3);% node[above] {$y(t)/y(0)$};
    \foreach \i in {0.1,0.2,...,0.9} \draw (0cm,\i cm) -- (-0.1cm,\i cm);
    \draw (0,0.5) -- (-0.15,0.5) node[left] {0.5};
    \draw (0,1.0) -- (-0.15,1.0) node[left] {1.0};
    %
    \draw (0,0) -- (1,1);
    \draw plot (\x,{1 - exp(-\x)});
    \node (exp) at (1.3,0.2) {$1 - e^{-t/\tau  }$};
    \node (lin) at (0.35,1.1) {$t/\tau$};
    \draw[thin,<-] (0.8,0.8) -- (lin);
    \draw[thin,<-] (1.0,0.63) -- (exp);
  \end{tikzpicture}
