how to improve the coupling coefficient of on-chip CMOS transformer

[noanob]

HI all
I built a transformer made by two spiral inductor in ADS Momentum and simulate the coupling coefficient of the transformer . Its K is only around 0.4 at in 5GHz.
I tried different layout method such as symmetric and stacked layout . I also increased the size the two spiral inductor , my inductance L1 and L2 is around 0.2nH for a 100um*100um layout , Is this inductance too small?

My substrate is like :
Cond1: 4um Sigma-4.51E7 S/m
SiO2 upper [VIA]diel 4.51E7
COnd2: 0.66um ( I varied this from 3um to 0.66um) sigma = 4.51E7
SiO2 Lower : 5um Er=4
Silicon Er=11.9 , 6.67S/m , 500um

How can I get a K>0.8 ?
Thanks

 

[vfone]

To increase the coupling coefficient you have to increase somehow the number of turns of the inductor.
0.2nH seems to be very small, even for 5GHz.

 

[BigBoss]

If you decrease the distance between the spirs, coupling will be improved.
Use minimum DR for you process and try..

 

[Hamid.Kiumarsi]

Reduce trace's width. Of course this will reduce also Q but will increase K.
Your IL is a function of K^2.Q1.Q2. SO you have a trade-off in choosing the width. Also you have to consider the current affordability of transformer

 

[renzhixiong]

Hi noanob,We can only get S parameters data from ADS Momentum results.Therefore I want to know how to use S parameters to count specs of trnasformer ,such as ILm,Efficiency,k,.etc. Many Thx!