EEVblog Electronics Community Forum
EEVblog => EEVblog Specific => Topic started by: EEVblog on April 23, 2014, 10:43:56 pm
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What's inside a $13K Agilent Source Measure Unit capable of 15fA and 100nV resolution?
Plus triaxial cables, and low current measurement connection.
Data Sheet: http://cp.literature.agilent.com/litweb/pdf/5990-7009EN.pdf (http://cp.literature.agilent.com/litweb/pdf/5990-7009EN.pdf)
User Manual
Connection Guide: http://cp.literature.agilent.com/litweb/pdf/B2900-90090.pdf (http://cp.literature.agilent.com/litweb/pdf/B2900-90090.pdf)
Component Datasheets:
Dual MOSFET http://www.fairchildsemi.com/ds/FD/FDS8978.pdf (http://www.fairchildsemi.com/ds/FD/FDS8978.pdf)
OPA1611 Audio Opamp http://www.ti.com/lit/gpn/opa1611 (http://www.ti.com/lit/gpn/opa1611)
ISO7240A Isolators: http://www.ti.com/lit/gpn/iso7240a (http://www.ti.com/lit/gpn/iso7240a)
ADS8202 Diff Amp: http://www.analog.com/static/imported-files/data_sheets/AD8208.pdf (http://www.analog.com/static/imported-files/data_sheets/AD8208.pdf)
ADS1675 24bit ADC: http://www.ti.com/lit/gpn/ads1675 (http://www.ti.com/lit/gpn/ads1675)
30N06 MOSFET: https://www.fairchildsemi.com/ds/FQ/FQP30N06.pdf (https://www.fairchildsemi.com/ds/FQ/FQP30N06.pdf)?
EEVblog #607 - Agilent B2912A Source Measure Unit SMU Teardown (https://www.youtube.com/watch?v=pKX50E_14MQ#ws)
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Use it to characterize that old selenium diode you have lying around!
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I have a Keithley 2400 SMU and its probably one of the most useful tools we have in our lab. We use it to drive many of our plasma probes for characterizing the performance of the Ion drives we test with and measuring high impedance loads. Personally if I ever find a SMU on ebay for "cheap" I'll get one for my personal lab. They are great tools more people should have them.
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"Shhhmmmuuuu"??? ?? I think you're making that up :)
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There is an RF version, called SMURF :o
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Is it me or one of the leads from the 10 meg (big green flat) resistors is not soldered? at min 25:53
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Great video, :clap: looking forward to the practical applications follow on. If it were possible would be really interesting to see an old school model for comparison.
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Great teardown Dave :-+ It would be interesting to see a zener curve done on the screen or just a leakage test like I did on the 2450 here (http://youtu.be/o13e5LWsPTI?t=6m5s) to compare the interfaces between the Agilent and the Keithley.
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Great teardown Dave :-+ It would be interesting to see a zener curve done on the screen or just a leakage test like I did on the 2450 here (http://youtu.be/o13e5LWsPTI?t=6m5s) to compare the interfaces between the Agilent and the Keithley.
I don't know about the keithley, but I can say the UI on the Agilent kinda sucks :--
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I definitely hope to see a video of it in use. I've always wanted an SMU.
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I think this might be the machine that I am most jealous of you for having. :'(
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UI tool from website for Kei2400 is sucks too, but who cares, SMU gear is on that level already when custom software/LabView app pays for itself.
SMU is a great addition for lab, expensive but handy for lot of applications. In worst case you can you it as 4-quadrant power supply :-DD
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Wow, talk about NSFW. 8) That's one hell of an instrument. 10fA! Is there a little dude in there somewhere counting the electrons as they pass by? I couldn't see him...
10fA is one single electron per 16µs, if anyone didn't realize that.
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Is that CR2032 leaking at 54:40 ?
https://www.youtube.com/watch?v=pKX50E_14MQ#t=3280 (https://www.youtube.com/watch?v=pKX50E_14MQ#t=3280)
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10fA is one single electron per 16µs, if anyone didn't realize that.
(https://i.imgur.com/GFIjZbC.gif)
*shouts*: Companies, keep throwing expensive equipment at Dave! We need more than Agilent to hop on board :D
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Is that CR2032 leaking at 54:40 ?
https://www.youtube.com/watch?v=pKX50E_14MQ#t=3280 (https://www.youtube.com/watch?v=pKX50E_14MQ#t=3280)
I don't think so -- looks more like a surface finish + reflections. I know lithium primaries have a lot of energy, but the CR chemistry AFAIK is current-limited and mostly indestructible.
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Interesting review. The 24 bit 4 MS/s ADC is not that expensive as I expected, Digikey sells it for $38.79. I wonder if you could just connect some long wire to it and then demodulate longwave AM radio broadcast signals, all digitally, without external filtering.
PS: Is it still Agilent or Keysight? Strange that if you click on the products link on the keysight.com homepage, it just links to agilent.com, with the same old Agilent Technologies logo. Looks like they are not really serious about the name change.
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Wohoo! Vias under D2PAKs - I've been doing that for years and everyone keeps telling me it's like totally WAY bad. Now I feel vindicated! :phew:
Awesome bit of kit that...
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What about measuring uCurrent? :)
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Wohoo! Vias under D2PAKs - I've been doing that for years and everyone keeps telling me it's like totally WAY bad. Now I feel vindicated! :phew:
Is there a reason why is it supposed to be a bad idea?
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Wohoo! Vias under D2PAKs - I've been doing that for years and everyone keeps telling me it's like totally WAY bad. Now I feel vindicated! :phew:
Is there a reason why is it supposed to be a bad idea?
As Dave said, mainly solder leeching through the vias taking the paste away from the top layer pad where it's supposed to be. I've never experienced a problem with this though even with via holes of up to 0.6mm diameter. I usually place thermal vias in four quadrants under the pad, leaving a cross shape of bare pad under the component. But vias directly under smaller pads (<1206) are indeed a bad idea, they do leech away noticeable amounts of solder.
Some people say that tenting the via with soldermask on the other side of the board is a good idea to help prevent the solder leeching, but I believe this is a terrible idea - the tenting traps air in the via which expands and explodes when the component is reflowed leading to voids in the solder joint between the component and pad. I now leave the underside vias untented but with minimal pad annulus so the solder can leech through but not spread on the bottom layer too far. Top-side tenting or plugged vias are great, but add cost.
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Nice video, I would like to see a further video about the unit in operation.
I also missed details about the low current source / measure circuitry, perhaps I have to follow the video for a 2nd time.
Frank
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would be a shame not to see it working given you have some test fixtures
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It would be interesting to see how far your teardown has moved the calibration. Ask Agilent if they can give you the numbers later.
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These videos of teardowns of extremely high-end 'analog' equipment are my favorites. I learn a lot about best design practice. I've never thought of the need to shield a cooling fan for EMI, but it makes sense. Please do a video on the use of this SMU.
This Agilent is a work of art. I love the way they designed it to be repaired, and the thermal management. The surface residue on the boards is surprising, but I guess it is only cosmetic. Is it flux or a residue from the silk screen?
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First I thought that's a heater on a fan, to maintain constant temperature inside unit, but since it's exhaust fan, no, just a shield :)
Surprised to see MiniFit JR connector on output side, and no triax on this SMU, and still spec'd as 10fA!
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To FrankBuss: Interesting idea to use the 24-bit A/D for software defined radio. I didn't know they made 24-bit devices that fast. You'll certainly need a front-end with a high pass filter. If you don't use a bandpass filter you'll also get a lot of high frequency noise that 'folds-in'. Keep in mind that the most advanced FlexRadio SDR's use two 16-bit 250 MS/sec A/D's with bandpass filters.
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Wow, talk about NSFW. 8) That's one hell of an instrument. 10fA! Is there a little dude in there somewhere counting the electrons as they pass by? I couldn't see him...
10fA is one single electron per 16µs, if anyone didn't realize that.
I did not... that's amazing :)
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I really wonder what kind of thermal performance they can get out of those TO263's. If it's all linear (high precision, low noise) device, and can deliver up to 30W, and need a fan ducted heatsink, I can imagine they can probably dissipate 30W on the PCB as well?
edit: it can deliver 105mA up to 21-210V. So at 22V out, and assuming 245V input, then (245-22)*0.105 = 23W.
I'm very tempted to back-mount a TO220 heatsink (with 1 flat side) and see how much thermal resistance the PCB "adds", and via-stitch the hell out of the copper planes.
If I'd use a 5K/W heatsink, how much would the overall resistance become? 10K/W? Less/more?
Even with 10K/W, you can probably dissipate 6-8W surface-mount at room temperature. Maybe even more with a fan directly on the heatsink..
Would be interesting to try for some really compact cooling..
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Is it good practice to wind the long wires up like that? Sure looks like candy sticks but I heard of computer systems malfunctioning because they wound data bus wires around cassis parts or something like that causing inductance and magnetic interferances. :-//
PS.: Or doesnt it matter as long as its only a couple not winding around a center piece of metal?
PPS: Got it.: :-DD http://en.wikipedia.org/wiki/Twisted_pair (http://en.wikipedia.org/wiki/Twisted_pair) Sorry this post has become obsolete.
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Dave mentioned that one might find a rack mounted version of this on a manufacture assembly run. I can see this used in a companies R&D lab, but what use would it have in unit assembly/testing? Seems like it's main use is characterizing individual components? Other applications would be?
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Awesome bit of gear! Thanks for the elaborate teardown Dave! And yes I would certainly want to see it in use.
I can't help but pausing the video many times and just stare at the electronics and even mechanical stuff that just shouts quality engineering through and through, trying to take it in. Would love to be part of a team designing such an instrument one day. (A man can dream, right 8))
As for semiconductor testing during manufacturing that is the domain of big test machines with custom fixtures for each type of IC. I've seen quite a few different ones at NXP Nijmegen where they test the testers and test algorithms before they go life on the actual testers in their manufacturing plants. On the other hand those testers are basically 'just' a rack of 4 quadrant powersupplies/SMUs PCBs on a backplane connected up to the actual test head.
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The U1103 in minute 26 could be a ADG1212YCPZ the datasheet says that the branding is S08
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That 24-bit ADC would make an amazing multimeter front end. With a span of +/- 2V you could have a quarter of a microvolt resolution.
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That 24-bit ADC would make an amazing multimeter front end. With a span of +/- 2V you could have a quarter of a microvolt resolution.
The Keithley 2450 has 10pV resolution on the saved data on the lowest range. Displayed measure resolution is 10nV. But it is not as accurate as my Fluke 8846A as seen in my 2450 SMU review here (https://www.eevblog.com/forum/testgear/keithley-2450-sourcemeter-review/msg368281/#msg368281)
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To FrankBuss: Interesting idea to use the 24-bit A/D for software defined radio. I didn't know they made 24-bit devices that fast. You'll certainly need a front-end with a high pass filter. If you don't use a bandpass filter you'll also get a lot of high frequency noise that 'folds-in'. Keep in mind that the most advanced FlexRadio SDR's use two 16-bit 250 MS/sec A/D's with bandpass filters.
Good idea to use a bandpass filter. Maybe I should use 100 kHz as the lower limit, for filtering most noise like mains, sferic (http://en.wikipedia.org/wiki/Radio_atmospheric) (on the other hand might be interesting to measure sferic) etc., and the upper limit well below the nyquist limit. Then it should be possible to do the rest digitally.
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I added some pictures to compare the Agilent B2912A SMU with Keithley 2636B SMU. It has similar construction with heatsink tunnel in center of instrument shared with two identical modules.
For obvious reasons I do not want to dissassemble it fully.
The power supply is Densei-Lambda.
When I was looking for new SMU the Agilent was also one candidate.The spec are quite simmilar.
The controlling instrument by LXI or by embeded TSP is difficult, I rather control instrument by LabView.
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more photos
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Plesa, those are interesting pictures. Are the vertically oriented boards all digital system? It would seem they would suffer from a large temperature gradient top to bottom.
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Dave mentioned that one might find a rack mounted version of this on a manufacture assembly run. I can see this used in a companies R&D lab, but what use would it have in unit assembly/testing? Seems like it's main use is characterizing individual components? Other applications would be?
Verifying that randomly selected components from a production run match the reference characterization?
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There is only one board oriented vertically, the rest is oriented horizontal. The SMU boards are oriented both way and on bottom side of instrument is power supply, digital board and one board which is connected between Densei-Lambda power supply and SMU analog boards.
The instrumet fan is almost silent after few minutes when it is powered up it became quite noisy.
I can make some Flir images if you want.
added front end pictures.
I was quite surprissed with huge oldschool 4 terminal power resistor in front end enclosure VCS302 0R1.On front end is quite popular LMC66.
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Beautiful! Thank you, Dave.
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First post here..
First of all Dave, Have watched a fair amount of your videos... upset you never finished your Power Supply...
Anyways On Topic... Since he never finished his lab supply (and I am needing one) I decided to build one (I am an Industrial guy so dont get around "professionally" a lot of the more traditional electronics stuff a lot), I am still in the design phase and figured out this SMU is the same thing that im trying to build (goal was 1uA not 10fA though).
I learned a lot from this video and will incorporate their design practices into my design (who knows might make it OH or put it on Kickstarter)
So has anyone heard of a "Service Manual" for this guy? (Doubt it lol) ... :-DD
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Hi Dave,
I could not recommend this SMU for chiplevel semiconductor device measurements and I think for general purpose SMU jobs in the board level domain it is too expensive.
The panel show a 10fA number but that is only the resolution. At 10nA range the offset is 50pA or 5000ppm. That is because of the hole design compromize where the high current range MOSFETs present leakage to the output path. That is because I guess the relays are not used to isolate the current ranges. I had issues in the past where the temperature rise in high current range change the gate leakage current impact in a subsequent low current range. That could be fixed by reversing the sequence in testing but makes the device stepping slower. I tought that it would be better to use relays there. Optional these could be inactive by software if speed is prefered.
The second issue is that todays small semiconductors have temperature time constants which are 10-100x faster than 10us. So the curves are distorted by the various temperature effects. These are important only in the higher current range relative to the maximum current of the devices but there is no trade built into the SMU instrument speed versus resolution.
So for semiconductor SMU jobs it is not specific designed for and for discrete device testing it is too expensive.
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Hi Dave,
I enjoy your videos thanks. Those triaxial connectors that are used on the external test enclosure connections are the same that are used on a jet aircraft data distribution bus, ie MIL-STD-1553. i have worked on those in the past. the coax used with them was 78 Ohm. After watching your video i then realized that maybe they were using a similar "guard" screen system on the aircraft. Aircraft power was 400Hz with the chassis the return. but i think the 1553 data bus is a differential system. anyway that is first time i have seen those connectors any where else other than on aircraft. they could be used on land vehicles, space craft etc too...
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Hi Dave,
I could not recommend this SMU for chiplevel semiconductor device measurements and I think for general purpose SMU jobs in the board level domain it is too expensive.
The panel show a 10fA number but that is only the resolution. At 10nA range the offset is 50pA or 5000ppm. That is because of the hole design compromize where the high current range MOSFETs present leakage to the output path. That is because I guess the relays are not used to isolate the current ranges. I had issues in the past where the temperature rise in high current range change the gate leakage current impact in a subsequent low current range. That could be fixed by reversing the sequence in testing but makes the device stepping slower. I tought that it would be better to use relays there. Optional these could be inactive by software if speed is prefered.
The second issue is that todays small semiconductors have temperature time constants which are 10-100x faster than 10us. So the curves are distorted by the various temperature effects. These are important only in the higher current range relative to the maximum current of the devices but there is no trade built into the SMU instrument speed versus resolution.
So for semiconductor SMU jobs it is not specific designed for and for discrete device testing it is too expensive.
I have the same opinion, that it is too expensive. I do not thing that banana socket is best chioce for the precision measurement. On 2636 it is much more better, lowest range 100pA. For basic semiconductor characterization is better choice the Keithley picoammeter 6485 which is about 1,5k USD but without supply. Or their dual picoammeter 6482 with integrated supply (30V ) for about 4,5k USD.
Hi Dave,
I enjoy your videos thanks. Those triaxial connectors that are used on the external test enclosure connections are the same that are used on a jet aircraft data distribution bus, ie MIL-STD-1553. i have worked on those in the past. the coax used with them was 78 Ohm. After watching your video i then realized that maybe they were using a similar "guard" screen system on the aircraft. Aircraft power was 400Hz with the chassis the return. but i think the 1553 data bus is a differential system. anyway that is first time i have seen those connectors any where else other than on aircraft. they could be used on land vehicles, space craft etc too...
There is much more triaxial connectors available - not only BNC basis (Fischer, Lemo they have their own solution), the old ones has only two lugs and can be destroyed plugging it to normal BNC, thats why has been made the tri-lug triaxial connector.
For purposes you mentioned were propably used connectors with different insulation materials (cheaper).
I was also quite surprised when I saw the triax during Mike teardown of the Fluorescence Spectrometer. For low level measuremnts should be used only connectors with PTFE insulation.
It is quite similar with cables, you can find the cheap triaxial cable, but it is not useable for low level measuremets in pA range.
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For comparison the Keithley 617 have
10fA Error at the 200pA Range
instead of
50pA Error at the 10nA range
That shows that the choosen SMU architecture is limited and the bad thing is that is more a matter of some (# ranges) relays.
There was some hint that it is not designed by agilent but bought. Is there a link?
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There is much more triaxial connectors available - not only BNC basis (Fischer, Lemo they have their own solution), the old ones has only two lugs and can be destroyed plugging it to normal BNC, thats why has been made the tri-lug triaxial connector.
For purposes you mentioned were propably used connectors with different insulation materials (cheaper).
I was also quite surprised when I saw the triax during Mike teardown of the Fluorescence Spectrometer. For low level measuremnts should be used only connectors with PTFE insulation.
It is quite similar with cables, you can find the cheap triaxial cable, but it is not useable for low level measuremets in pA range.
Here is a hint from the 617 manual about the cable material to minimize current noise in the fA range.
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Just to give the full picture, in a Triax the middle is not always the guard as described by David here
https://www.youtube.com/watch?feature=player_detailpage&v=pKX50E_14MQ#t=3034 (https://www.youtube.com/watch?feature=player_detailpage&v=pKX50E_14MQ#t=3034)
In my Keithley 220 the outside is the chassis, the middle is the ground and the center is the output.
See here for details:
https://www.eevblog.com/forum/testgear/keithley-220-output-triax-connector-mod/msg397850/#msg397850 (https://www.eevblog.com/forum/testgear/keithley-220-output-triax-connector-mod/msg397850/#msg397850)
the guard is provided in the back with a banana female, separated from the Triax cable.
I don´t see why the Keithley 220 engineers decided to do that. Maybe the chassis can not always be used as a return conductor for a tiny current.
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There is much more triaxial connectors available - not only BNC basis (Fischer, Lemo they have their own solution), the old ones has only two lugs and can be destroyed plugging it to normal BNC, thats why has been made the tri-lug triaxial connector.
For purposes you mentioned were propably used connectors with different insulation materials (cheaper).
I was also quite surprised when I saw the triax during Mike teardown of the Fluorescence Spectrometer. For low level measuremnts should be used only connectors with PTFE insulation.
It is quite similar with cables, you can find the cheap triaxial cable, but it is not useable for low level measuremets in pA range.
Here is a hint from the 617 manual about the cable material to minimize current noise in the fA range.
http://www.keithley.com/knowledgecenter/knowledgecenter_pdf/LowLevMsHandbk.pdf (http://www.keithley.com/knowledgecenter/knowledgecenter_pdf/LowLevMsHandbk.pdf)
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Nice teardown :)
Please do a working review, Agilent measurement has some basic videos, but not much in depth.
Would like to see leakage of a glass body diode in the dark and when illuminated - remembering Bob Pease had something on this 20-odd years ago.
ETA: Keithley works around cable noise by pushing the front end out to the DUT:
http://www.keithley.com/products/dcac/sensitive/highresistance/?mn=6430 (http://www.keithley.com/products/dcac/sensitive/highresistance/?mn=6430)
I always spelled it shmoo :D
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Would like to see leakage of a glass body diode in the dark and when illuminated - remembering Bob Pease had something on this 20-odd years ago.
My video of just that on the Keithley 2450 SMU
https://www.youtube.com/watch?v=o13e5LWsPTI (https://www.youtube.com/watch?v=o13e5LWsPTI)
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The second issue is that todays small semiconductors have temperature time constants which are 10-100x faster than 10us. So the curves are distorted by the various temperature effects.
It is fascinating to see inside this instrument and to see the accuracy they can measure to for dc - but for many semiconductor devices such as FETs in particular the resultant curves are only useful for estimating a dc bias point.
Many devices have charge trapped in deep energy levels (ironically generally associated physically with the surface of the semiconductor) which have time constants much slower than RF so when the device is operated under RF the curves it follows can be completely different from those measured under slow dc conditions.
This is a subject close to my heart because the small company I started with two others joined with another small company to develop a pulsed measurement system to take measurements faster than the time constants.
The difference can be spectacular, on some SiC power devices charge trapped in surface states led to the nicely spaced dc curves (as would be measured on a SMU) collapsing more or less into a single curve as the gate voltage was pinned by the surface charge.
So making super accurate dc measurements of semiconductor devices and then using them to fit a large-signal spice like model or even just to estimate the class A power you might get out can lead to spectacular errors much larger than those of using a cheap bench power supply and pocket DVMs to get the same curves!
The characteristic curves depend on where the device is biased and at the rate at which you then measure them.
This is not true of all devices, some we looked at showed very close agreement between pulsed and dc measurements. There will always be some difference because of thermal effects.
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Would like to see leakage of a glass body diode in the dark and when illuminated - remembering Bob Pease had something on this 20-odd years ago.
My video of just that on the Keithley 2450 SMU
https://www.youtube.com/watch?v=o13e5LWsPTI (https://www.youtube.com/watch?v=o13e5LWsPTI)
Excellent. Thanks!
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The second issue is that todays small semiconductors have temperature time constants which are 10-100x faster than 10us. So the curves are distorted by the various temperature effects.
It is fascinating to see inside this instrument and to see the accuracy they can measure to for dc - but for many semiconductor devices such as FETs in particular the resultant curves are only useful for estimating a dc bias point.
Many devices have charge trapped in deep energy levels (ironically generally associated physically with the surface of the semiconductor) which have time constants much slower than RF so when the device is operated under RF the curves it follows can be completely different from those measured under slow dc conditions.
This is a subject close to my heart because the small company I started with two others joined with another small company to develop a pulsed measurement system to take measurements faster than the time constants.
The difference can be spectacular, on some SiC power devices charge trapped in surface states led to the nicely spaced dc curves (as would be measured on a SMU) collapsing more or less into a single curve as the gate voltage was pinned by the surface charge.
So making super accurate dc measurements of semiconductor devices and then using them to fit a large-signal spice like model or even just to estimate the class A power you might get out can lead to spectacular errors much larger than those of using a cheap bench power supply and pocket DVMs to get the same curves!
The characteristic curves depend on where the device is biased and at the rate at which you then measure them.
This is not true of all devices, some we looked at showed very close agreement between pulsed and dc measurements. There will always be some difference because of thermal effects.
Could you give us some info about your product or product planning. I have interest in special purpose device testing as well as modelling of semiconductor effects which affect our products. Foundries like to surpress this critical informations because only some customers have to work with these and most others will be in fear and finally the effort will give no return.
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Could you give us some info about your product or product planning. I have interest in special purpose device testing as well as modelling of semiconductor effects which affect our products. Foundries like to surpress this critical informations because only some customers have to work with these and most others will be in fear and finally the effort will give no return.
It is ten years since I left the field but from my previous experience things probably haven't changed much!
The instrument we produced was called a DiVA and it allowed you to set a bias point and then measure curves from that bias point by pulsing voltage changes to both the gate and drain (for FETs) Voltages returning to the bias point after each pulse. The shortest pulse was (by todays standards) a fairly slow 100nsecs but we found that this was fast enough to be faster than the time constants of the deep levels for trapped charge as well as avoiding thermal changes (the other reason for curves shifting).
Accent, who bought the technology from our little company and for whom I worked for five years were themselves bought out and in the process I think the DiVA ceased to be produced. Various others were producing rival products (such as Keithley I think) and I'd guess that these are still made.
You could probably use a dual channel waveform generator and a scope and a lot of tedious fiddling around to perform the same sort of measurements though this might limit you to a fairly small voltage range. You have to take some care as timing can be an issue (for instance if you have a power limited device biased at high VDS in an almost off state and you want to pulse down to an on state at low VDS you must be sure not to have the gate pulse lead the drain pulse else you might kill the device).
There are a couple of curves (Figures 4.1 and 4.2) in this Masters Thesis
http://etd.fcla.edu/SF/SFE0000249/CharlesBaylisFinalSubmissionMastersThesis.pdf (http://etd.fcla.edu/SF/SFE0000249/CharlesBaylisFinalSubmissionMastersThesis.pdf)
The thesis also contains a few references but I just tried the following Microwave Journal article we wrote :
http://www.microwavejournal.com/articles/3414-the-importance-of-the-current-voltage-characteristics-of-fets-hemts-and-bipolar-transistors-in-contemporary-circuit-design (http://www.microwavejournal.com/articles/3414-the-importance-of-the-current-voltage-characteristics-of-fets-hemts-and-bipolar-transistors-in-contemporary-circuit-design)
and I see that the figures are all wrong - instead of being our figures they are diagrams of on-wafer rf probes as far as I can see!! :palm:
If you have stacks of cash you could use Auriga/Agilent kit :
http://www.home.agilent.com/agilent/editorial.jspx?cc=GB&lc=eng&ckey=1963507&nid=-11143.0&id=1963507 (http://www.home.agilent.com/agilent/editorial.jspx?cc=GB&lc=eng&ckey=1963507&nid=-11143.0&id=1963507)
but if you're using a foundry the biggest problem may be getting access to test devices.
If you google pulse I-V measurement system you'll find quite a lot of things come up eg. Maury Microwaves system:
http://www.amcad-engineering.com/IMG/File/Pulsed%20IV_product_feature.pdf (http://www.amcad-engineering.com/IMG/File/Pulsed%20IV_product_feature.pdf)
though I see that only goes down to 200 nsecs which is probably a little slow.
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Could you give us some info about your product or product planning. I have interest in special purpose device testing as well as modelling of semiconductor effects which affect our products. Foundries like to surpress this critical informations because only some customers have to work with these and most others will be in fear and finally the effort will give no return.
It is ten years since I left the field but from my previous experience things probably haven't changed much!
The instrument we produced was called a DiVA and it allowed you to set a bias point and then measure curves from that bias point by pulsing voltage changes to both the gate and drain (for FETs) Voltages returning to the bias point after each pulse. The shortest pulse was (by todays standards) a fairly slow 100nsecs but we found that this was fast enough to be faster than the time constants of the deep levels for trapped charge as well as avoiding thermal changes (the other reason for curves shifting).
Accent, who bought the technology from our little company and for whom I worked for five years were themselves bought out and in the process I think the DiVA ceased to be produced. Various others were producing rival products (such as Keithley I think) and I'd guess that these are still made.
You could probably use a dual channel waveform generator and a scope and a lot of tedious fiddling around to perform the same sort of measurements though this might limit you to a fairly small voltage range. You have to take some care as timing can be an issue (for instance if you have a power limited device biased at high VDS in an almost off state and you want to pulse down to an on state at low VDS you must be sure not to have the gate pulse lead the drain pulse else you might kill the device).
though I see that only goes down to 200 nsecs which is probably a little slow.
Thank you for the excellent work.
Yes, 200ns is too slow. The problem is more with small foundry devices instead of big packaged discrete devices because the thermal time constant is in proportion to the square of the dimension of the device.
Instead of using a Bias-T I think it is better to use a interface circuit direct attached to the probe head. The issue to serve various devices is more in the current domain, like gummel-plot or subthreshold. So a high current range input on Source/Emitter and ARB driven Gate/Base and Drain/Collector voltage sources are the most effective. The high current range is implemented by an an OpAmp with a number electronical switched feedback resistors. The frequency compensation and speed is then dependend on the current range but that is the trade which I expected everywhere. This output is then feed to the ADC and the hole stuff is put into script control. I guess that with 12-bit DAC + 12-bit ADC the cycle time could go up to 10ns for the mA ranges. The critical point for the speed vs. current is the passive virtual ground capacitance of the probe head. So using a small separate board direct on the probe head with the OpAmp and MUX-Rs should give the best trade.
A side effect is that also Q(V) could be measured by using the low current input on the gate and driving the ramps on source and drain.
Here the DUT Circuit from AMCAD&Maury
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Instead of using a Bias-T I think it is better to use a interface circuit direct attached to the probe head.
You're very right about bias-Ts especially ones designed for dc rather than pulsed. We didn't use them with the DiVA. But to fair on the designers of that system, the bias-Ts are to allow large-signal S-parameters I guess (though I can't remember if large signal S-parameters are actually large signal S-parameters or small-signal S-parameters measured at each point within the time of the pulse.)
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The part Dave had mentioned in the video (25') is a Sanyu's reed relay. :D
SORRY about this reply, my English sucks :(
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It looks like this http://www.sanyu-usa.com/highinsulation2-en.html (http://www.sanyu-usa.com/highinsulation2-en.html) or something from here http://www.sanyu-usa.com/category/products/reed-relays2/high-insulation-wet-en (http://www.sanyu-usa.com/category/products/reed-relays2/high-insulation-wet-en)
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Hi Guys,
I just went through the teardown of the B2912A. Truly impressive device, but the teardown got me thinking of how this SMU actually works. The power supply inside generates + and - 245V, fine. Then it uses two constant current sources, one sourcing towards the +245V and the other to the -245V. The current sources are basically made the same as a constant current electronic load, a mosfet and OPA and a shunt resistor. All fine and dandy, but this is the part that interests me. If you have the two current sources, how can the SMU operate in the constant voltage mode? For example, how can you order it to generate a 12V output, if there is no load connected? Even if you order the top current source to let only 1uA through, the voltage on the output would be (almost) the full 245V. Anyone has an idea how the CV part works?
Ivo
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We have a B2912A in school and it was really nice to see the inside of this instrument.
Thanks
I have been watching your videos for a long time, just registered here today.