  Most electromechanical devices are in two-dimensional metallic drums under
high tensile stress, which causes increased mechanical frequency and quality
factor. However, high mechanical frequencies lead to small zero-point
displacements $x_{\rm zp}$, which limits the single-photon interaction rate
$g_0$. For applications which demand large $g_0$, any design with increased
$x_{\rm zp}$ is desirable. It is shown that a patterned drum by spiral shape
can resolve this difficulty, which is obtained by a reduction of mechanical
frequency while the motion mass is kept almost constant. An order of magnitude
increase in $g_0$, and agreement between simulations and interferometric
measurements is observed.
