  This letter proposes a direct construction for cross Z-complementary sets
(CZCSs) with flexible lengths and a large zero correlation zone (ZCZ). CZCS is
an extension of the cross Z-complementary pair (CZCP). The maximum possible ZCZ
width of a CZCP is half of its sequence length. In this letter, for the first
time, a generalized Boolean function based construction of CZCSs with a large
number of constituent sequences and a ZCZ ratio of $2/3$ is presented. For
integers $m$ and $\delta$, the proposed construction produces CZCS with length
expressed as $2^{m-1}+2^\delta$ ($0 \leq \delta <m-1,m\geq 4$), where both odd
and even lengths CZCS can be obtained. Additionally, the constructed CZCS also
feature a complementary set of the same length. Finally, the proposed
construction is compared with the existing works.
