What are lowest leakage current and smallest burden voltage electronic switches  - Page 1
Forum section: electronics / beginners

author: MathWizard
author_rank: Super Contributor
timestamp: August 17, 2025, 08:58:12 pm
content: I'm just wondering what's considered a low leakage E-switch these days, like simple JFET's or MOSFET's, and whats the lowest VDS they can achieve if they are only conducting say uA's ?I have a bunch of real MMBF4117 JFET's, and I think they have around nA's of off-state leakage current, and VDS of 100's of mV for a few uA. Which is pretty good for some things.I'm upgrading an op-amp test jig I made, and it will take a lot of ranges switches, especially if I add all separate ranges for quad op-amps. I've found some mechanical rotary switches on Digikey that might be ok.But here if I'm trying to measure down to 100's of pA of input current and and uV's of input offset voltage, which then gets magnified by 2 op-amp's. So I'd want switch leakage currents way smaller than typical JFET's or MOSFET's that I know of. And I'd want way smaller VCE or VDS voltages when on too.If they were was cheaper, I'd get a bunch of reed relays or similar, like old DMM's use. I guess I should look up relays too, maybe there are some cheap ones that would do.

author: MathWizard
author_rank: Super Contributor
timestamp: August 21, 2025, 02:19:57 am
content: I'm wondering more about discrete parts, or array IC's even, so I don't mean like the latest memory cell that can stay charged for years or decades.

author: exe
author_rank: Unknown
timestamp: August 21, 2025, 07:31:56 am
content: What is the required blocking voltage?

author: Kleinstein
author_rank: Super Contributor
timestamp: August 21, 2025, 07:51:28 am
content: A problem with most discrete MOSFETs is that they essentially all have some overvoltage protection for the gate and this extra zener adds leakage for the GS link. So ready made CMOS switches have a slight advantage here. There are some low leakage Maxim parts, like max326-329.One has to compromise between on resistance and leakage. The lowest leakage is found with high R_on. With CMOS switch chips there are also the protection "diodes" to the supply, however these can be build so that there leakage largely compensates.A problem with very low leakage parts is that the specs (especially the maximum values) may be measurment limits as testing in the sub pA range is expensive (needs time for settling). So the data-sheets along may not tell the whole story.Normally the xxx4117 should be good for the 1 pA range at room temperature.Many reed relays are actually not that low in leakage - not sure why but many of the cheap ones a leaky (e.g. 100 Gohms range).

author: exe
author_rank: Unknown
timestamp: August 21, 2025, 01:04:11 pm
content: There are a few mosfets from, e.g., NXP that do not show zenner at the gate, e.g.:https://assets.nexperia.com/documents/data-sheet/2N7002.pdfCompare with this one (and do not confuse similar part numbers):https://assets.nexperia.com/documents/data-sheet/NX7002AK.pdf. The later has "ESD protected" in datasheet, the former not.It's a bit tedios job to check every datasheet, but I did find a few devices without esd-protection here:https://www.nexperia.com/products/mosfets/small-signal-mosfets#/p=1,s=0,f=,c=,rpp=,fs=0,sc=c4ab5d,so=des,es=.I bought a few, but I hasn't tested them for leakage yet.Also, rumors say small mosfets without protection are extremely sensitive to ESD. I read elsewhere that a company had failure rate of 70% in production when they used unprotected mosfets. I checked with my ESD tester, just moving on a chair can create 100V easily, way above what a gate can handle. So, I always ground myself and humidify the air before removing ESD-sensitive components. There are air ionizers for that purpose.

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2025, 02:18:11 pm
content: The 2N4117 is the standard for low leakage JFETs and can be better than 1 picoamp. There are comparable 3N series small signal MOSFETs but I think they have much higher drain leakage.Texas Instruments has CMOS analog switches like the MUX6119 which are suppose to be almost as good as, and maybe better than a 2N4117.

author: exe
author_rank: Unknown
timestamp: August 21, 2025, 02:51:12 pm
content: I think I had a good experience with CD405* (e.g., CD4053) switches. If I find one, I'll try to measure leakage... on breadboard).They are not great linearity, and parameters different between manufacturers.... But they do have a level shifter.Similar device from NXP: 74HC4316PW.112The only thing is, datasheets are "conservative", so real performance needs to be verified. If I find one, I'll try to measure leakage current.

author: Simmed
author_rank: Frequent Contributor
timestamp: August 21, 2025, 04:31:32 pm
content: i wonder how low it will go if one were to series 2 of these

author: David Hess
author_rank: Super Contributor
timestamp: August 21, 2025, 05:57:11 pm
content: Quote from: edavid on August 21, 2025, 04:27:26 pmMany datasheets do not say, but I have a Siliconix datasheet which claims a typical 0.2 picoamp drain cutoff current with a note that drain cutoff current is not a registered with JEDEC. Buy some from different sources and test them.Quote from: Simmed on August 21, 2025, 04:31:32 pmI have done that before to good effect, but it was more complicated than merely placing them in series. I drive the connection between them to reduce the drain-to-source voltage across the low leakage one to zero.An example of this is applying the switch to the virtual summing node of an operational integrator. Since the inverting input is always at a known voltage, that being the same as the non-inverting input, the point between the two transistor can be driven to the same voltage to control leakage when the switch is turned off. If a MOSFET is used, then the gate can be driven to this voltage also. A MOSFET with the same voltage at each terminal has little leakage even if it is not a low leakage MOSFET.Quote from: exe on August 21, 2025, 02:51:12 pmThey are only tested down to like 1 microamp, so buyer beware and qualify them yourself.

author: exe
author_rank: Unknown
timestamp: August 21, 2025, 08:31:26 pm
content: So I tried to measure the on-resistance and off-leakage of CD74HC4053E. Quick-n-dirty, on a breadboard. I touched IC with my hands (but I tried to be careful), and before that it spent a few years in the drawer unprotected. The on-resistance was 56 ohm at 4.8V supply.The leakage... Idk, I tried to measure, my DIY meter showed -1pA at 9.5V supply from battery (it has some ~5pA permanent offset, after connecting the IC it became like 4pA). I don't know why it's negative, and not confident that I measured it correctly, but definitely the leakage is small.I had to use battery as when supplying from a PSU my meter was showing 10nA, which is clearly wrong.This is not the second time I measure the leakage of a CD405*, and it is consistently small. Before I used NXP/Nexperia/whatever device, now it's... TI?EDIT: forgot to say, I measured leakage at ~3V (from CR2032)

author: RJSV
author_rank: Super Contributor
timestamp: August 22, 2025, 02:51:50 am
content: (Since my suggestion isn't directly practical right now, I've waited a bit, for other replies to come.)Nano-tech or micro-machines have not (heavily) been deployed, yet, or I'm not at least reading much news. A micro-mechanical electric switch (SPDT or similar) would have control-able manufacturing, of the contact material and essentially have similar qualities as a human operated manual switch.You perhaps can gain some quality controls using good reed relays as well, assuming the market has available info on contact materials.But certainly, your approach would help avoid a lot of arcane semiconductor stuff, like base-emitter (diode) voltage on inputs, etc.Course problems with expense and size exists with reed relays, but at least let's you focus on the proper contact material. Assuming the makers can supply the variations you seek.

author: MathWizard
author_rank: Super Contributor
timestamp: August 23, 2025, 06:20:20 pm
content: OK so the 4117 should be lower leakage than I said, yeah I was just eyeballing a graph in the datasheet. But for the large burden voltages, I was going by LTSpice. The ones I bought lately from LCSC were from OnSemihttps://www.onsemi.com/pdf/datasheet/mmbf4117-d.pdfI bought them more for high frequency stuff, but yeah they are pretty good at low leakage stuff too.10G ohms sounds huge to me, but yeah 10V/10GR is 1nA, and I just about trust my DMM's down to nA's, it makes me wonder how much leakage current is on typical PCB's. I have to get back to that low voltage and current book I was reading.I'll have to try a few experiments w/ some of my parts, and see what the leakage is like. And maybe try making some trace guarding with buffers.There's lots of stuff I'd make, where pA's or nA's of leakage doesn't matter, I'll have to check out some of the new CD logic IC's.

author: David Hess
author_rank: Super Contributor
timestamp: August 23, 2025, 10:47:08 pm
content: Quote from: MathWizard on August 23, 2025, 06:20:20 pmThe 4117 is *the* low leakage JFET. The 4416 is an RF JFET commonly used for 100+ MHz high impedance inputs. I always get the two confused.QuoteA normal multimeter can be used as a picoammeter with a 10 megohm current shunt in voltage mode, allowing current measurements down to 100 or 10 picoamps.QuotePicoamps is where things get real. I have a multimeter to repair which has 2+ nanoamps of leakage, apparently in the circuit board, when it needs to be more like 10 picoamps to meet its specifications.

author: RJSV
author_rank: Super Contributor
timestamp: August 24, 2025, 12:38:39 am
content: Conformal coatings can help with surface contaminates, plus some of the aerospace and high voltage users use various rinse fluids, again for cleaning. Sometimes, the motivation for extreme cleaning is to help have a short pump-down, when prep'ing for helium leak testing.They go to unusual lengths, like doing the 2 hour vacume pump-down while your unit is enclosed in an oven, for maximum removal of contaminates.What's your book ? (Sorry if already described).Oh, and don't forget geometry of construction, avoid sharp points or other shapes that encourage leakage, (on surface). That's keeping your field strengths at minimum, again on surface features.

author: MathWizard
author_rank: Super Contributor
timestamp: August 26, 2025, 01:12:13 pm
content: I can't find it now but it was some book on low voltage and current measurments, I also have some good app. notes on that by a few sources. I should be reading all that too. The other book was one a greybeard on here recommended,Building Mathematical Functions with Circuits_Burr_Brown_1976, it's over 8MB so I can't post it.Once I finish sorting/choosing resistors for my upgraded op-amp test jig, then I'll have to try some JFET switches. These still have very low capacitance, I mainly got them for a DC-100MHz probe I made, but only tried with ebay 2N5485's or similar so far.But yeah they use a bunch of them in my 5.5D Keithley DMM, as well as reed relay's. And some how they cancel out the leakage currents. I'll have to look at all those circuits again with way more op-amp experience since I last worked on it.I hardly use current mode on my SDM3065X. I really should try directly measuring some op-amp bias currents.

author: exe
author_rank: Unknown
timestamp: August 29, 2025, 07:51:29 pm
content: I repeated my measurements with a more sensitive ammeter. And I still can't measure the leakage. Though one thing is, it seems the leakage current is... negative. And it's in 1pA ballpark. Like, about 0.3-0.7pA, not sure because readings are not stable. My theory is that, since switch is powered by +9.5V, there is leakage to positive supply that cancels out (and dominates!) leakage to ground.PS the on-resistance of switches is 46 ohm when CD4053 is supplied from 9.5V battery.

author: exe
author_rank: Unknown
timestamp: August 30, 2025, 05:17:32 pm
content: Just for fun I measured leakage of BS170 nfet. With gate shorted to source, drain-source leakage is ~3pA at 3V. Gate-source leakage was below 1pA.