Panasonic schottky......or not ?

In the Panasonic schottky diode catalog, there are a number of parts that don't state that the parts are schottky, though the top of the catalog page still carries the schottky barrier diode heading. They share similar part numbering structures and descriptions as parts in the ultrafast rectifier line.

Schottky parts are fabbed using the same 'planar' process, but the 'epitaxial' description seems out of place here.

A possible confusion is aggravated by Panasonic's tendency to describe the reverse recovery time of schottky parts, when positioned in the standard Trr test circuit, where performance is basically an RC effect.

eg:

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Does anyone out there have actual experience in weeding out small signal and rectifier schottkys from UFRs in the Panasonic line-up?

I've only ever used a few of their schottky parts. Conventional fast diodes are easily supplied by more prominent mfrs, so there's never been an issue. Vendors seem only to have the same ambiguous data sheets to draw from. They appear to have no trouble correcting Panasonic's faulty package drawing designations - but descriptions of 'schottky or not' follows the data sheet page catalog section's header.

RL

Reply to
legg
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That data sheet says "schottky" at the top. The forward and reverse curves sure look schottky.

I don't think that epitaxial is incompatible with schottky.

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John Larkin         Highland Technology, Inc 

lunatic fringe electronics
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Reply to
John Larkin

The V_forward graph looks like a Schottky.

George h.

Reply to
George Herold

So does the reverse curve, both in magnitude and shape.

Schottkies can have real reverse recovery, if they have a p-n guard ring that conducts at higher currents. But Panasonic may just be a little weird.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

Huh, thanks, I never knew Schottkys were so leaky in reverse. There must be some physics reason for that...?

Re: p-n guard ring, well that's doubly beyond my knowledge, though edge effects in photodiodes is something I see all the time.

George H.

Reply to
George Herold

Dunno about the physics, but they are very leaky and leakage increases smoothly with voltage. Regular diodes are more constant-current leakage then a steep zener thing.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

It's a steep avalanche thing. Zener breakdown only happens for breakdown voltage less than about five volts.

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Bill Sloman, Sydney
Reply to
bill.sloman

Sure, Schottkys are leaky. If they weren't, there will be far less use for silicon diodes.

Reply to
krw

Vf = 350mV at 100mA, near the 200mA max, has to be Schottky.

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Reply to
Winfield Hill

A diffused guard ring creates the builtin field of an unbiased PN junction, in the right direction to pull surface dirt away from the (sensitive) edge regions of the Schottky metallization. The same kind of thing helps HV diodes (lessens leakage and aging effects), when simple passivation isn't enough.

Half the problem in semiconductors is that you can make resistors, and amplifiers, and switches, easily, but insulators have to be reverse biased PN junctions, and wires have to be mapped onto one surface (if two wires have to cross, there's cost or trickery to do that).

The other half, is that the finished item has all the working parts buried, but unburied surfaces ALSO work, usually against your design goals. You can't keep surfaces absolutely clean. Some of those surfaces have to sink heat, through bear grease, too..

Guard rings are a behind-the-scenes necessity, and (from the physics point of view) rather elegant.

Reply to
whit3rd

Of course it's a Schottky diode, but can't a metal contact be deposited on epitaxially grown silicon?

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John Larkin         Highland Technology, Inc 

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Reply to
John Larkin

One reason early diodes (of the 50s and 60s) were so fragile (relatively low voltage rating, avalanche causes death): where the junction meets the surface, it's either cleaved (in which case, who knows what dirt, and particular dopants and surface states, are going on), or early planar diffused with similar problems, poor material purity, homogeneity and such.

Today, even schottky diodes are rated for avalanche (though not all that much, it's just the guard rings), which sure is handy.

Tim

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Seven Transistor Labs, LLC 
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Reply to
Tim Williams

Lower barrier. :^)

Or something to do with the metal being full of free charge carriers, I don't remember.

The high voltage kinds (over 100V I think) leak almost as little as the PN kind, because of another bit of tech: the schottky junction is placed on a pillar, surrounded by gate oxide and metallization (or just bare, using ambient electric field without needing extra field plates). Basically they put a depletion MOS in series with it, increasing Vf and Rs a little bit once again (hey, no free lunch), in exchange for much higher breakdown voltage and lower leakage.

Tim

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Reply to
Tim Williams

Right that was my first guess. (But I'm not sure.)

This is OK

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Says it's due to majority carriers on metal side. I should make my own Schottky I-V graph, that would help.

George H. (I'll take Sze home tonight and read chapter 5 again.)

Reply to
George Herold

And a very differently shaped curve.

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John Larkin         Highland Technology, Inc 
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Reply to
John Larkin

OK I got my parts ordered and did an I-V. Well two, first I did a

1N5711 then a beefier 1N5817, leakage was nowhere near 1 uA. 1-10 nA range. (100's of mV/100 Meg ohm) The little 1N5711 leaked about twice as much. (go figure)

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It's a semi-log plot (with log of the voltage) so it looks different from the panasonic data sheet. (making it semi-log the other way and it's mostly just a flat line.)

George H.

Reply to
George Herold

Sure. Epitaxial silicon is no different from bulk.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Well, to the extent that a schottky junction cares. (There are important differences with epitaxy, but that's subtle compared to "does it junction" or not.)

Tim

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Reply to
Tim Williams

No, there aren't, except for doping, and not necessarily even that. Epi is monocrystalline silicon, grown on top of the bulk with no boundary. That's the whole point of the exercise--building clean, dislocation-free junctions with way more control than old-timey diffusion or even ion implantation.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
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Reply to
Phil Hobbs

Yeah, that's what I mean :)

Tim

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Reply to
Tim Williams

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