  THz polarization control upon generation is a crucially missing
functionality. THz spintronic emitters based on the inverse spin Hall effect
allow for this by the strict implicit orthogonality between their magnetization
state and the emitted polarization. This control was up till now only
demonstrated using cumbersome external magnetic field biasing to impose a
polarization direction. We present here for the first time an efficient voltage
control of the polarization state of terahertz spintronic emitters. Using a
ferromagnetic spin pumping multilayer exhibiting simultaneously strong uniaxial
magnetic anisotropy and magnetostriction in a crossed configuration, an emitter
is achieved where in principle the stable magnetization direction can be fully
and reversibly controlled over a 90$^\circ$ angle span only by an electric
voltage. To achieve this, an engineered rare-earth based ferromagnetic
multilayer is deposited on a piezoelectric
$\textrm{(1-x)[Pb(Mg}_\textrm{0.33}\textrm{Nb}_\textrm{0.66})\textrm{O}_\textrm{3}\textrm{]-x[PbTiO}_\textrm{3}\textrm{]}$
(PMN-PT) substrate. We demonstrate experimentally a reversible 70$^\circ$ THz
polarization rotation by sweeping the substrate voltage over 400V. This
demonstration allows for a fully THz polarization controlled ISHE spintronic
terahertz emitter not needing any control of the magnetic bias.
