On Tuesday, October 15, 2013 1:04:01 PM UTC-4, Phil Hobbs wrote:> On 10/15/2013 12:48 PM, George Herold wrote: >=20 > > On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >=20 > >> On 10/15/2013 01:36 AM, Jim Thompson wrote:<snip>> >> There are all kinds of CV measurements. MOSFET threshold is just > >> one--for instance, you can get the doping density vs. depth in a diode > >> by measuring C(V). I've learned a lot of interesting things about >=20 > >> photodiodes that way, but it's more commonly used for incoming > >> inspection of wafers--you use a mercury or (nowadays) gallium electrod=e> >> for the top contact. > >> > > > > Hi Phil, Say do you have a good reference for the C-V doping density t=echnique.> > > > I find a bit in Sze's book. I guess I can follow the references in the=re.> > > > George H. >=20 >=20 >=20 > It's pretty simple. The physics is that (in the 1D approximation), in=20 > order to move the edge of the depletion zone from z to z+dz, you have to==20> create a sheet of charge >=20 > d sigma =3D rho dz >=20 > and the capacitance change is >=20 > dC =3D A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is==20> the dielectric constant of fully depleted silicon. > =20 > The E field goes as the integral of the sheet charge elements >=20 > E =3D 1/epsilon integral (0 to z) rho(z) dz >=20 > and V is the line integral of the E field. >=20 > V =3D integral (0 to z) E(z) dz >=20 > So you get z from the capacitance, and then rho from the second=20 > derivative of V with respect to z. Haven't got time to do the=20 > derivation properly, but that's more or less how it goes. >=20 > There are fine points having to do with where you take the origin of=20 > voltage (probably the contact potential of the junction) and Debye=20 > shielding, so some care is needed.Thanks Phil... (ask for a reference and I get a mini-dissertation :^) There were guys doing this measurement back in grad school, but I didn't pa= y any attention. There's some distinction between high frequency and low= frequency response too. But there's there's lots on the web, just a matte= r of removing the dregs and dross. =20 George H.>=20 >=20 >=20 > What I found was that a lot of my favourite high-speed and=20 >=20 > high-linearity PDs have a buried layer of higher doping, like an APD. >=20 >=20 >=20 > Boonton 72BDs are all the go. >=20 >=20 >=20 > Cheers >=20 >=20 >=20 > Phil Hobbs >=20 >=20 >=20 > --=20 >=20 > Dr Philip C D Hobbs >=20 > Principal Consultant >=20 > ElectroOptical Innovations LLC >=20 > Optics, Electro-optics, Photonics, Analog Electronics >=20 >=20 >=20 > 160 North State Road #203 >=20 > Briarcliff Manor NY 10510 >=20 >=20 >=20 > hobbs at electrooptical dot net >=20 > http://electrooptical.net
Never Buy Maxim (again)
Started by ●October 13, 2013
Reply by ●October 15, 20132013-10-15
Reply by ●October 15, 20132013-10-15
On 10/15/2013 04:43 PM, Robert Baer wrote:> Phil Hobbs wrote: >> On 10/15/2013 12:35 AM, miso wrote: >>> On 10/14/2013 1:06 PM, John Larkin wrote: >>>> On Mon, 14 Oct 2013 12:54:52 -0700, miso <miso@sushi.com> wrote: >>>> >>>>> On 10/13/2013 12:34 PM, John Larkin wrote: >>>>>> >>>>>> These opamps, like most Maxim parts, have nonstandard pinout. I >>>>>> built a test >>>>>> fixture to measure Cin. With power off, I measured 1.4 pF on the >>>>>> non-inverting >>>>>> input pin. >>>>> Who measures capacitance of a part that is powered down? Doh! There >>>>> are >>>>> diodes that need to be reverse biased ya know. >>>> >>>> Of course, but I measured it first, powered down. Why not? >>>> >>>> It wouldn't work like an opamp closed-loop, and I need that to measure >>>> the powered-up capacitance. >>>> >>>>> >>>>> Do you have someone who works for you that is, well you know, a >>>>> competent electrical engineer? Perhaps you are not suited for >>>>> electrical >>>>> engineering. Have you considered software? >>>> >>>> >>>> I've written a lot of code, but I prefer hardware design. >>>> >>>> All the things that I posted are true. >>>> >>>> Quit whining and show us some gear that you've designed... full of >>>> Maxim chips no doubt. >>>> >>>> >>> The input capacitance of an op amp, or really any input pin, is a >>> combination of stray capacitance to a field and junction capacitance. >>> [The stray capacitance to a field is a combination of capacitance in the >>> package, bonding wire, and interconnect over substrate.] It makes no >>> sense to measure the capacitance unless the junctions are properly >>> biased. Seriously, this is component eval 101. >>> >>> Not only do you insure the device is powered up properly, but you need >>> to insure the the SMU will not force the input out of normal operation. >>> And of course there is the issue of nulling the test fixture >>> capacitance. Low level measurement is a skill. >>> >>> It is pretty rare a chip is at fault. When the dust settles, it is >>> nearly always pilot error. That is why eval boards are sold. Think about >>> it. The unit is in production. Even a loser product will sell a few >>> hundred thousand units a year, so why does it work for everyone else but >>> not you? Pilot error. >>> >>> You might want to consider how sample stock at a semi is maintained. >>> When the part is deemed sellable, tested units from that lot are put >>> into the sample stock. Over the years, the sample stock can be pretty >>> old. Now if there is an electrical specification change in the >>> datasheet, the sample stock will be pulled and retested. But otherwise, >>> the sample stock is from the very first batch. Now it will meet the >>> electrical specification, but it could possibly be different in some >>> manner not tested. Processes shift, wafer vendors change, etc. It is an >>> analog world. This variance shouldn't be a big deal, but if you depend >>> on some parameter that is not tested, don't expect the current >>> production to match the sample stock. >>> >>> A lot of those op amp designs were from Gain Technology. Arizona. Need I >>> say more? Actually they had a few good engineers, but over all mostly >>> wankers. >> >> Some of us care about input capacitance a lot. For TIAs (photodiode or >> otherwise) the op amp's high frequency noise current is dominated by its >> input noise voltage differentiated by the total capacitance on the >> summing junction. >> >> The best op amps I know about have Cin of about 1.4 pF, so something >> down at 0.4 pF with reasonable voltage noise would be pretty interesting >> for some things. For instance, I recently did a front end for a surface >> voltage tool, which basically holds a probe tip a couple of mils above a >> spinning wafer. The work function depends very strongly on surface >> contamination, so you can map out sub-monolayer oil slicks and such like. >> >> Dropping the input capacitance by a whole pF would have been nice. >> >> Cheers >> >> Phil Hobbs >> >> > ...and, obviously, a driven guard was of little help. >Oh, the whole thing was bootstrapped right to the eyeballs, otherwise the op amp capacitance wouldn't have been that big a deal. You can't usefully bootstrap an op amp's supplies and noninverting input at high frequency, I wouldn't think--its differential input signal would go away, so it wouldn't do anything except measure the quality of the bootstrap. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●October 15, 20132013-10-15
Phil Hobbs wrote:> On 10/15/2013 12:35 AM, miso wrote: >> On 10/14/2013 1:06 PM, John Larkin wrote: >>> On Mon, 14 Oct 2013 12:54:52 -0700, miso <miso@sushi.com> wrote: >>> >>>> On 10/13/2013 12:34 PM, John Larkin wrote: >>>>> >>>>> These opamps, like most Maxim parts, have nonstandard pinout. I >>>>> built a test >>>>> fixture to measure Cin. With power off, I measured 1.4 pF on the >>>>> non-inverting >>>>> input pin. >>>> Who measures capacitance of a part that is powered down? Doh! There are >>>> diodes that need to be reverse biased ya know. >>> >>> Of course, but I measured it first, powered down. Why not? >>> >>> It wouldn't work like an opamp closed-loop, and I need that to measure >>> the powered-up capacitance. >>> >>>> >>>> Do you have someone who works for you that is, well you know, a >>>> competent electrical engineer? Perhaps you are not suited for >>>> electrical >>>> engineering. Have you considered software? >>> >>> >>> I've written a lot of code, but I prefer hardware design. >>> >>> All the things that I posted are true. >>> >>> Quit whining and show us some gear that you've designed... full of >>> Maxim chips no doubt. >>> >>> >> The input capacitance of an op amp, or really any input pin, is a >> combination of stray capacitance to a field and junction capacitance. >> [The stray capacitance to a field is a combination of capacitance in the >> package, bonding wire, and interconnect over substrate.] It makes no >> sense to measure the capacitance unless the junctions are properly >> biased. Seriously, this is component eval 101. >> >> Not only do you insure the device is powered up properly, but you need >> to insure the the SMU will not force the input out of normal operation. >> And of course there is the issue of nulling the test fixture >> capacitance. Low level measurement is a skill. >> >> It is pretty rare a chip is at fault. When the dust settles, it is >> nearly always pilot error. That is why eval boards are sold. Think about >> it. The unit is in production. Even a loser product will sell a few >> hundred thousand units a year, so why does it work for everyone else but >> not you? Pilot error. >> >> You might want to consider how sample stock at a semi is maintained. >> When the part is deemed sellable, tested units from that lot are put >> into the sample stock. Over the years, the sample stock can be pretty >> old. Now if there is an electrical specification change in the >> datasheet, the sample stock will be pulled and retested. But otherwise, >> the sample stock is from the very first batch. Now it will meet the >> electrical specification, but it could possibly be different in some >> manner not tested. Processes shift, wafer vendors change, etc. It is an >> analog world. This variance shouldn't be a big deal, but if you depend >> on some parameter that is not tested, don't expect the current >> production to match the sample stock. >> >> A lot of those op amp designs were from Gain Technology. Arizona. Need I >> say more? Actually they had a few good engineers, but over all mostly >> wankers. > > Some of us care about input capacitance a lot. For TIAs (photodiode or > otherwise) the op amp's high frequency noise current is dominated by its > input noise voltage differentiated by the total capacitance on the > summing junction. > > The best op amps I know about have Cin of about 1.4 pF, so something > down at 0.4 pF with reasonable voltage noise would be pretty interesting > for some things. For instance, I recently did a front end for a surface > voltage tool, which basically holds a probe tip a couple of mils above a > spinning wafer. The work function depends very strongly on surface > contamination, so you can map out sub-monolayer oil slicks and such like. > > Dropping the input capacitance by a whole pF would have been nice. > > Cheers > > Phil Hobbs > >..and, obviously, a driven guard was of little help.
Reply by ●October 15, 20132013-10-15
On Mon, 14 Oct 2013 19:15:29 -0700, Jim Thompson <To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote:>On Mon, 14 Oct 2013 22:13:11 -0400, krw@attt.bizz wrote: > >>On Mon, 14 Oct 2013 17:27:04 -0700, Jim Thompson >><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >> >>>On Mon, 14 Oct 2013 19:15:15 -0400, krw@attt.bizz wrote: >>> >>>>On Mon, 14 Oct 2013 13:06:00 -0700, John Larkin >>>><jlarkin@highlandtechnology.com> wrote: >>>> >>>>>On Mon, 14 Oct 2013 12:54:52 -0700, miso <miso@sushi.com> wrote: >>>>> >>>>>>On 10/13/2013 12:34 PM, John Larkin wrote: >>>>>>> >>>>>>> These opamps, like most Maxim parts, have nonstandard pinout. I built a test >>>>>>> fixture to measure Cin. With power off, I measured 1.4 pF on the non-inverting >>>>>>> input pin. >>>>>>Who measures capacitance of a part that is powered down? Doh! There are >>>>>>diodes that need to be reverse biased ya know. >>>>> >>>>>Of course, but I measured it first, powered down. Why not? >>>>> >>>>>It wouldn't work like an opamp closed-loop, and I need that to measure >>>>>the powered-up capacitance. >>>>> >>>>>> >>>>>>Do you have someone who works for you that is, well you know, a >>>>>>competent electrical engineer? Perhaps you are not suited for electrical >>>>>>engineering. Have you considered software? >>>>> >>>>> >>>>>I've written a lot of code, but I prefer hardware design. >>>>> >>>>>All the things that I posted are true. >>>>> >>>>>Quit whining and show us some gear that you've designed... full of >>>>>Maxim chips no doubt. >>>> >>>>What do you expect. He worked for Maxim. ...probably maxim.com. >>> >>>So you don't know what you measure under power-down conditions either? >> >>Clueless. > >You are?Why don't you just show what a jerk you are, again, and plonk me, again? Idiot.
Reply by ●October 15, 20132013-10-15
On Tue, 15 Oct 2013 19:18:47 -0400, krw@attt.bizz wrote:>On Mon, 14 Oct 2013 19:15:29 -0700, Jim Thompson ><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: > >>On Mon, 14 Oct 2013 22:13:11 -0400, krw@attt.bizz wrote: >> >>>On Mon, 14 Oct 2013 17:27:04 -0700, Jim Thompson >>><To-Email-Use-The-Envelope-Icon@On-My-Web-Site.com> wrote: >>> >>>>On Mon, 14 Oct 2013 19:15:15 -0400, krw@attt.bizz wrote: >>>> >>>>>On Mon, 14 Oct 2013 13:06:00 -0700, John Larkin >>>>><jlarkin@highlandtechnology.com> wrote: >>>>> >>>>>>On Mon, 14 Oct 2013 12:54:52 -0700, miso <miso@sushi.com> wrote: >>>>>> >>>>>>>On 10/13/2013 12:34 PM, John Larkin wrote: >>>>>>>> >>>>>>>> These opamps, like most Maxim parts, have nonstandard pinout. I built a test >>>>>>>> fixture to measure Cin. With power off, I measured 1.4 pF on the non-inverting >>>>>>>> input pin. >>>>>>>Who measures capacitance of a part that is powered down? Doh! There are >>>>>>>diodes that need to be reverse biased ya know. >>>>>> >>>>>>Of course, but I measured it first, powered down. Why not? >>>>>> >>>>>>It wouldn't work like an opamp closed-loop, and I need that to measure >>>>>>the powered-up capacitance. >>>>>> >>>>>>> >>>>>>>Do you have someone who works for you that is, well you know, a >>>>>>>competent electrical engineer? Perhaps you are not suited for electrical >>>>>>>engineering. Have you considered software? >>>>>> >>>>>> >>>>>>I've written a lot of code, but I prefer hardware design. >>>>>> >>>>>>All the things that I posted are true. >>>>>> >>>>>>Quit whining and show us some gear that you've designed... full of >>>>>>Maxim chips no doubt. >>>>> >>>>>What do you expect. He worked for Maxim. ...probably maxim.com. >>>> >>>>So you don't know what you measure under power-down conditions either? >>> >>>Clueless. >> >>You are? > >Why don't you just show what a jerk you are, again, and plonk me, >again? Idiot.Me too! Plonk me too! -- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
Reply by ●October 15, 20132013-10-15
On Tue, 15 Oct 2013 16:29:32 -0700, John Larkin <jlarkin@highlandtechnology.com> wrote:>Me too! Plonk me too!--- Why ask someone else to do what you could so easily do yourself. ;) -- JF
Reply by ●October 15, 20132013-10-15
On Tue, 15 Oct 2013 10:51:18 -0700, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 10/15/2013 01:32 PM, John Larkin wrote: >>> ...snip.... >> >> I've been meaning to try a parallel-plate cap as a displacement >> transducer. Measuring nanometers ought to be easy. >> >> > > You want a differential cap to take out the thermal expansion. > > Cheers > > Phil Hobbs >company in England makes an instrument using capacitance to measure displacement. Incredible resolution in the range of 20 to 50 ppm, that's like 25 nm at a distance of 0.1 inch? One application is to use it to adjust distances to focus an e-beam on a substrate and take into account the roughness of the substrate. Very interesting technique to do it. I'll have to see if I'm limited by an NDA before I can describe the methodology. I do remember to use it properly I had the PCB shop do five PCB's at a cost of $25,000 - very difficult: big cutouts, big plated holes, blind vias, buried vias etc etc plus had to be vacuum compatible. The PCB house was so proud of their work, they put a sample PCB in their lobby to show potential customers their capability at doing really 'difficult' PCBs
Reply by ●October 15, 20132013-10-15
On 10/15/2013 8:45 PM, RobertMacy wrote:> On Tue, 15 Oct 2013 10:51:18 -0700, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/15/2013 01:32 PM, John Larkin wrote: >>>> ...snip.... >>> >>> I've been meaning to try a parallel-plate cap as a displacement >>> transducer. Measuring nanometers ought to be easy. >>> >>> >> >> You want a differential cap to take out the thermal expansion. >> >> Cheers >> >> Phil Hobbs >> > > > company in England makes an instrument using capacitance to measure > displacement. Incredible resolution in the range of 20 to 50 ppm, that's > like 25 nm at a distance of 0.1 inch? One application is to use it to > adjust distances to focus an e-beam on a substrate and take into account > the roughness of the substrate. Very interesting technique to do it. > I'll have to see if I'm limited by an NDA before I can describe the > methodology. I do remember to use it properly I had the PCB shop do five > PCB's at a cost of $25,000 - very difficult: big cutouts, big plated > holes, blind vias, buried vias etc etc plus had to be vacuum compatible. > The PCB house was so proud of their work, they put a sample PCB in their > lobby to show potential customers their capability at doing really > 'difficult' PCBsQueensgate Instruments, maybe? They've been making picometer-resolution piezos in the 10-100 um range for some years now, but nothing in the 2.5 mm class. (They cost a lot, so I've only admired them from afar.) I have a 100-um class XY flexure stage that was made by Wye Creek Instruments, a garage operation run by Fred Scire and Clayton Teague of the NBS (as it then was). The piezo stacks run at 0-3 kV. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 USA +1 845 480 2058 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●October 15, 20132013-10-15
On Tue, 15 Oct 2013 17:54:55 -0700, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:> On 10/15/2013 8:45 PM, RobertMacy wrote: > ...snip... > Queensgate Instruments, maybe? They've been making picometer-resolution > piezos in the 10-100 um range for some years now, but nothing in the 2.5 > mm class. (They cost a lot, so I've only admired them from afar.) > > I have a 100-um class XY flexure stage that was made by Wye Creek > Instruments, a garage operation run by Fred Scire and Clayton Teague of > the NBS (as it then was). The piezo stacks run at 0-3 kV. > > Cheers > > Phil Hobbs > > >Yes, that's it. we were using their capacitor displacement sensor in the 25-50 nm range [from memory]
Reply by ●October 15, 20132013-10-15
On Tue, 15 Oct 2013 18:45:23 -0500, John Fields <jfields@austininstruments.com> wrote:>On Tue, 15 Oct 2013 16:29:32 -0700, John Larkin ><jlarkin@highlandtechnology.com> wrote: > > >>Me too! Plonk me too! > >--- >Why ask someone else to do what you could so easily do yourself. ;)SED has become like a leftist organization... the bombastic egotistical ignorant claim supremacy and chastise those of us who know how semiconductors function when we point out their errors. I _will_not_stop_ pointing out the ignorant whether they froth (or is it foam ?:-) at the mouth or not. ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
