We propose monolithically integrated electro-optical modulators based on thin-film x-cut barium titanate that exhibit large modulation bandwidth and operate at voltages compatible with complementary metal-oxide-semiconductor technology. The optical and radio frequency parameters of the modulator are systematically simulated, calculated, and optimized, respectively. Our simulation includes the evaluation of single-mode conditions, the separation distance between the electrode edge and the waveguide edge, bending loss, optical field distribution, and half-wave voltage-length product for optical parameters, and characteristic impedance, attenuation constant, radio frequency effective index, and -3d B modulation bandwidth for radio frequency parameters. By engineering both the microwave and photonic circuits, we have achieved high electro-optical efficiencies and group-velocity matching simultaneously. Our numerical simulation and theoretical analysis show that the half-wave voltage-length product was 0.48 V·cm, and the -3d B modulation bandwidths with a device length of 5 mm and 10 mm were 262 GHz and 107 GHz, respectively. Overall, our study highlights the potential of the proposed modulators for low driving voltage and high-performance optical communication systems.