4
\$\begingroup\$

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.

\$\endgroup\$
7
  • \$\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
    Commented 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
    Commented 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
    Commented Sep 29, 2022 at 14:51
  • \$\begingroup\$ What's special about the BSS138P? The one from Nexperia lists gate leakages of 100nA \$\endgroup\$
    – DKNguyen
    Commented 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
    Commented Sep 29, 2022 at 17:32

2 Answers 2

Reset to default
5
\$\begingroup\$

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

\$\endgroup\$
2
  • \$\begingroup\$ Thanks. Now it would be great if digikey/mouser could add IGSS or ESD-protection(YES/NO) to their checklist, too :) \$\endgroup\$
    – tobalt
    Commented 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\$
    – Stein Nesbakk
    Commented Sep 30, 2022 at 13:41
3
\$\begingroup\$

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

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.