  The quantum anomalous Hall effect in layered antiferromagnet MnBi$_2$Te$_4$
harbors a rich interplay between magnetism and topology, holding a significant
promise for low-power electronic devices and topological antiferromagnetic
spintronics. In recent years, MnBi$_2$Te$_4$ has garnered considerable
attention as the only known material to exhibit the antiferromagnetic quantum
anomalous Hall effect. However, this field faces significant challenges as
realizing quantized transport at zero magnetic fields depends critically on
fabricating high-quality device. In this article, we address the detrimental
influences of fabrication on MnBi$_2$Te$_4$ by simply depositing an AlO$_x$
thin layer on the surface prior to fabrications. Optical contrast and
magnetotransport measurements on over 50 samples demonstrate that AlO$_x$ can
effectively preserve the pristine state of the samples and significantly
enhance the anomalous Hall effect towards quantization. Scaling analysis
reveals the Berry curvature dominated mechanism of the anomalous Hall effect at
various magnetic configurations. By adjusting the gate voltage, we uncover a
gate independent antiferromagnetism in MnBi$_2$Te$_4$. Our experiment not only
pave the way for fabricating high-quality transport devices but also advance
the exploration of exotic quantum physics in 2D materials.
