The invention discloses a radiofrequency
LDMOS (laterally diffused
metal oxide semiconductor) device. A first
silicon epitaxial layer, a second
silicon epitaxial layer and a third
silicon epitaxial layer are stacked in order on the bottom surface of a silicon substrate, forming a silicon epitaxial layer. A drift area and a trench area are both formed in the third silicon epitaxial layer. The second silicon epitaxial layer is formed at the bottoms of the drift area and the trench area. The
doping density of the second silicon epitaxial layer is greater than that of the first and third silicon epitaxial
layers.
On resistance of the device and
breakdown voltage of a drain junction are adjusted by adjusting the
doping density of the third silicon epitaxial layer. The second silicon epitaxial layer is integrally provided with an inner RESURF structure (reduced
surface field) structure, used for decreasing
surface field of the drift area, thermal
carrier effect and improving reliability of the radiofrequency
LDMOS. The first silicon epitaxial layer helps maintain or increase the
breakdown voltage of the drain junction. The device has the advantages that source-drain stray
capacitance of the device can be improved, source-drain
on resistance can be reduced, drive current can be increased and radiofrequency characteristic of the device can be improved.