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I want to build a low-bias current (\$\ll\$1 pA) amplifier with a MOSFET for the fun of it. However, after testing the gate-source leakage current of some 2N7002s I was shocked that they leak roughly 1 nA at 1 V at room temperature, so are pretty useless for this project.

I then found this article on unprotected and ESD-protected MOSFET from Nexperia which seems to confirm that the leakage at this order of magnitude is indeed normal for ESD-protected MOSFETs, whereas unprotected MOSFETs should leak negligible currents at low bias.

After looking around a bit I couldn't find other unprotected parts other than the one mentioned in that article (BSS138P). Can you recommend a strategy for finding them ? Google just brought me back to that article and countless other MOSFETs, which weren't actually unprotected.

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  • \$\begingroup\$ I don't think there are any because they don't survive handling. If they did exist they'd probably in some unusual format like die-only. I know in some op-amps the method taken is that the ESD diodes are biased when power is applied to reduce the gate leakage. The LTC6268 does this. \$\endgroup\$
    – DKNguyen
    Sep 29, 2022 at 14:22
  • \$\begingroup\$ @DKNguyen Well the BSS138P is a usual SOT-23-3 part and seems stocked in the 1000s at the distributor of your trust. \$\endgroup\$
    – tobalt
    Sep 29, 2022 at 14:36
  • \$\begingroup\$ From the gate leakage specs on the BSS138P, it does seem like it has no/limited ESD protection. Most manufacturers probably wouldn't want to make a part like that because many customers require a certain level of ESD protection so that their products are manufacturable on a standard manufacturing line. Also, there are limited applications that would need such a part. So limited market, problematic part = no investment from semi companies. \$\endgroup\$
    – John D
    Sep 29, 2022 at 14:51
  • \$\begingroup\$ What's special about the BSS138P? The one from Nexperia lists gate leakages of 100nA \$\endgroup\$
    – DKNguyen
    Sep 29, 2022 at 17:29
  • \$\begingroup\$ @DKNguyen that is just the max. spec to which it is tested. Click the first link and view Fig. 4. \$\endgroup\$
    – tobalt
    Sep 29, 2022 at 17:32

2 Answers 2

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Can you recommend a strategy for finding them ?

Nexperia does have that column to select by (although hidden away).

  1. Go to Nexperia Small Signal
  2. Click "Add/Remove parameters"
  3. Check the "integrated gate-source ESD protection diodes" on the right hand side of the selection boxes

Disclaimer: I am an engineer at Nexperia

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  • \$\begingroup\$ Thanks. Now it would be great if digikey/mouser could add IGSS or ESD-protection(YES/NO) to their checklist, too :) \$\endgroup\$
    – tobalt
    Sep 30, 2022 at 10:15
  • \$\begingroup\$ No problem - if it's any help at all Nexperia also displays stock numbers and pricing on the website for every product :) \$\endgroup\$ Sep 30, 2022 at 13:41
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After no luck at Nexperia and Infineon (have to check each part individually), I found that Panjit have a column for ESD protection in the parametric search of their MOSFET products. So yes, they exist and plentiful even, but seems like almost no manufacturer/distributor is proud enough of them to provide search filters.

enter image description here

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