You can use 3:4 turn ratio, with 3 parallel and 4 series.
Too large turn ratio will decrease the coupling coefficient k.
In my opinion, the best on-chip transformer paper is
<Monolithic Transformers for Silicon RF IC Design> by J. R. Long, Vol 35, No. 9, JSSC 2000
vlsi_design wrote on Jan 14th, 2015, 7:30pm:Hi,
I want to design an onchip 1:5 balun. Can anyone suggest me books or IEEE papers?