How to optimize inductor EE25 core, target leakage inductance <100nH

[Johnson CGW]

In a recent customize inductor project, customer's requirement about EE25 core, target leakage inductance <100nH.
We have below 3 options:
1, Conventional Sandwich Winding(low cost)
Leakage: 142nH
Issue: Excessive interlayer capacitance causing ringing

2,Interleaved Section Winding
Leakage: 95nH ✓
Key improvement: 0.15mm interlayer insulation

3,Progressive Spiral Winding(high cost)
Leakage: 68nH ✓✓
Innovation: Dynamic wire diameter/spacing adjustment

Does anyone have better solution?

[mtwieg]

Can you explain what you mean by leakage inductance for an inductor (or is this a transformer)?

What's the required inductance/SRF?

[uer166]

Can you explain what you mean by leakage inductance for an inductor (or is this a transformer)?

It looks like a coupled inductor (flyback "transformer") from context, though OP should clarify

[ahbushnell]

Can you explain what you mean by leakage inductance for an inductor (or is this a transformer)?

It looks like a coupled inductor (flyback "transformer") from context, though OP should clarify

A coupled inductor is a transformer.  Not sure why you would put that in quotes. 

[uer166]

Can you explain what you mean by leakage inductance for an inductor (or is this a transformer)?

It looks like a coupled inductor (flyback "transformer") from context, though OP should clarify

A coupled inductor is a transformer.  Not sure why you would put that in quotes.

The distinction is important: a coupled inductor stores energy intentionally, while a transformer largely doesn't. A flyback transformer isn't a transformer in the normal definition. Not arguing semantics, rather explaining why I put it in quotes.

[ahbushnell]

Can you explain what you mean by leakage inductance for an inductor (or is this a transformer)?

It looks like a coupled inductor (flyback "transformer") from context, though OP should clarify

A coupled inductor is a transformer.  Not sure why you would put that in quotes.

The distinction is important: a coupled inductor stores energy intentionally, while a transformer largely doesn't. A flyback transformer isn't a transformer in the normal definition. Not arguing semantics, rather explaining why I put it in quotes.

Show me your reference on this?  They are both transformers.  I have built resonant systems and tuned the magnetizing inductance in the transformer which stores energy on each cycle.  I think calling it a coupled inductor is confusing.