High-performance terahertz emitters, which convert the femtosecond laser pulses into terahertz pulses, are essential for terahertz spectroscopy technology and terahertz wireless communication. Spintronic terahertz emitters based on ferromagnet/nonmagnet bilayers have attracted tremendous attention due to their high efficiency, ultra-broadband, low cost and high flexibility. Here, we systematically investigate the terahertz emission from polycrystalline topological insulator Bi ₂Te ₃/ferromagnetic CoFeB heterostructure grown by magnetron sputtering. The Bi ₂Te ₃/CoFeB heterostructure exhibits high efficiency of terahertz emission, and the polarization of terahertz waves can be controlled by the external magnetic field direction. The performance of Bi ₂Te ₃/CoFeB heterostructure is almost comparable to that of the Pt/CoFeB bilayer. In contrast, no terahertz emission is observed in the pure Bi ₂Te ₃or CoFeB film driven by femtosecond laser pulses, probably because the Bi ₂Te ₃prepared by sputtering is polycrystalline and the thickness of CoFeB is too thin. We also compare the performances of Bi ₂Te ₃/CoFeB grown on MgO, glass and high-resistivity silicon substrates, and find that the samples grown on MgO substrates exhibit the best emission performances. The glass substrate absorbs more terahertz waves than MgO substrate, resulting in a slightly weaker terahertz signal emitted from the Bi ₂Te ₃/CoFeB grown on the glass substrate. Although the absorption coefficient of high-resistivity silicon to terahertz waves is very small, the residual pump light excites the high-resistivity silicon to generate the photo-generated carriers, which change the conductivity of the high-resistivity silicon and reduce the transmittance of terahertz wave. We attribute the mechanism of the terahertz emission to the spin-charge conversion at the interface of Bi ₂Te ₃/CoFeB. The terahertz emission efficiency of our sample is expected to be able to be further improved by optimizing the samples. Moreover, with the sputtering method, it is possible to fabricate large area samples at low cost, which is critical for commercial applications.