You need to assign/push references to hashs/arrays, not the things themselves.

my %tmpF=();
my @tmpA;
push(@tmpA,"0001");
%tmpF->{ID}=@tmpA;
push(@$fieldobj,%tmpF);
[download]

should be

my %tmpF=();
my @tmpA;
push(@tmpA,"0001");
%tmpF->{ID}=\@tmpA;
#           ^
push(@$fieldobj,\%tmpF);
#               ^
[download]

Please read perlreftut to understand why you need references, and how they work.