On Tue, 15 Oct 2013 08:34:21 -0700, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>> ...snip... > 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 > >Sadly, I've found Maxim 'specs' to be more like "intereting goals" which some parts actually met.
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 01:36 AM, Jim Thompson wrote:> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: > >> >>>> >>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>> would anyone *not* want to measure the power-off capacitance, and then >>>> determine the C-V behavior? >>> >>> What "C-V behavior" are you referring to? >>> >>> ...Jim Thompson >>> >> >> CV is really a bad choice of words, but I don't think John means CV >> testings as in determining mosfet threshold. >> >> Tossing out buzzwords is generally not a good idea if you don't know >> what they mean. > > He's just throwing buzz words. He knows not of what he barfs. Are we > surprised? No. > > ...Jim Thompson >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 photodiodes that way, but it's more commonly used for incoming inspection of wafers--you use a mercury or (nowadays) gallium electrode for the top contact. 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
On 10/15/2013 11:46 AM, RobertMacy wrote:> On Tue, 15 Oct 2013 08:34:21 -0700, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >>> ...snip... >> 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 >> >> > > > Sadly, I've found Maxim 'specs' to be more like "intereting goals" which > some parts actually met.Too good to be true? I take it that that was what John wanted to find out. Of course engineering is divided into two sets of axes, real space and chart space. You can do a lot of amazing things as long as you never leave chart space. ;) 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
On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote:> On 10/15/2013 01:36 AM, Jim Thompson wrote: > > > On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: > > > >> > >>>> > >>>> I'm curious about things like ESD capacitance. Given a test setup, why > >>>> would anyone *not* want to measure the power-off capacitance, and then > >>>> determine the C-V behavior? > >>> > >>> What "C-V behavior" are you referring to? > >>> > >>> ...Jim Thompson<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 > photodiodes that way, but it's more commonly used for incoming > inspection of wafers--you use a mercury or (nowadays) gallium electrode > for the top contact. >Hi Phil, Say do you have a good reference for the C-V doping density technique. I find a bit in Sze's book. I guess I can follow the references in there. George H.> > > 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
On 10/15/2013 12:48 PM, George Herold wrote:> On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >> On 10/15/2013 01:36 AM, Jim Thompson wrote: >> >>> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: >>> >>>> >>>>>> >>>>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>>>> would anyone *not* want to measure the power-off capacitance, and then >>>>>> determine the C-V behavior? >>>>> >>>>> What "C-V behavior" are you referring to? >>>>> >>>>> ...Jim Thompson > <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 >> photodiodes that way, but it's more commonly used for incoming >> inspection of wafers--you use a mercury or (nowadays) gallium electrode >> for the top contact. >> > > Hi Phil, Say do you have a good reference for the C-V doping density technique. > > I find a bit in Sze's book. I guess I can follow the references in there. > > George H.It's pretty simple. The physics is that (in the 1D approximation), in order to move the edge of the depletion zone from z to z+dz, you have to create a sheet of charge d sigma = rho dz and the capacitance change is dC = A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is the dielectric constant of fully depleted silicon. The E field goes as the integral of the sheet charge elements E = 1/epsilon integral (0 to z) rho(z) dz and V is the line integral of the E field. V = integral (0 to z) E(z) dz So you get z from the capacitance, and then rho from the second derivative of V with respect to z. Haven't got time to do the derivation properly, but that's more or less how it goes. There are fine points having to do with where you take the origin of voltage (probably the contact potential of the junction) and Debye shielding, so some care is needed. What I found was that a lot of my favourite high-speed and high-linearity PDs have a buried layer of higher doping, like an APD. Boonton 72BDs are all the go. 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
On Tue, 15 Oct 2013 13:04:01 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/15/2013 12:48 PM, George Herold wrote: >> On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >>> On 10/15/2013 01:36 AM, Jim Thompson wrote: >>> >>>> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: >>>> >>>>> >>>>>>> >>>>>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>>>>> would anyone *not* want to measure the power-off capacitance, and then >>>>>>> determine the C-V behavior? >>>>>> >>>>>> What "C-V behavior" are you referring to? >>>>>> >>>>>> ...Jim Thompson >> <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 >>> photodiodes that way, but it's more commonly used for incoming >>> inspection of wafers--you use a mercury or (nowadays) gallium electrode >>> for the top contact. >>> >> >> Hi Phil, Say do you have a good reference for the C-V doping density technique. >> >> I find a bit in Sze's book. I guess I can follow the references in there. >> >> George H. > >It's pretty simple. The physics is that (in the 1D approximation), in >order to move the edge of the depletion zone from z to z+dz, you have to >create a sheet of charge > >d sigma = rho dz > >and the capacitance change is > >dC = A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is >the dielectric constant of fully depleted silicon. > >The E field goes as the integral of the sheet charge elements > >E = 1/epsilon integral (0 to z) rho(z) dz > >and V is the line integral of the E field. > >V = integral (0 to z) E(z) dz > >So you get z from the capacitance, and then rho from the second >derivative of V with respect to z. Haven't got time to do the >derivation properly, but that's more or less how it goes. > >There are fine points having to do with where you take the origin of >voltage (probably the contact potential of the junction) and Debye >shielding, so some care is needed. > >What I found was that a lot of my favourite high-speed and >high-linearity PDs have a buried layer of higher doping, like an APD. > >Boonton 72BDs are all the go. > >Cheers > >Phil HobbsI like the 72Bs with the analog meter. Very retro. -- 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 10/15/2013 01:15 PM, John Larkin wrote:> On Tue, 15 Oct 2013 13:04:01 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/15/2013 12:48 PM, George Herold wrote: >>> On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >>>> On 10/15/2013 01:36 AM, Jim Thompson wrote: >>>> >>>>> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: >>>>> >>>>>> >>>>>>>> >>>>>>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>>>>>> would anyone *not* want to measure the power-off capacitance, and then >>>>>>>> determine the C-V behavior? >>>>>>> >>>>>>> What "C-V behavior" are you referring to? >>>>>>> >>>>>>> ...Jim Thompson >>> <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 >>>> photodiodes that way, but it's more commonly used for incoming >>>> inspection of wafers--you use a mercury or (nowadays) gallium electrode >>>> for the top contact. >>>> >>> >>> Hi Phil, Say do you have a good reference for the C-V doping density technique. >>> >>> I find a bit in Sze's book. I guess I can follow the references in there. >>> >>> George H. >> >> It's pretty simple. The physics is that (in the 1D approximation), in >> order to move the edge of the depletion zone from z to z+dz, you have to >> create a sheet of charge >> >> d sigma = rho dz >> >> and the capacitance change is >> >> dC = A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is >> the dielectric constant of fully depleted silicon. >> >> The E field goes as the integral of the sheet charge elements >> >> E = 1/epsilon integral (0 to z) rho(z) dz >> >> and V is the line integral of the E field. >> >> V = integral (0 to z) E(z) dz >> >> So you get z from the capacitance, and then rho from the second >> derivative of V with respect to z. Haven't got time to do the >> derivation properly, but that's more or less how it goes. >> >> There are fine points having to do with where you take the origin of >> voltage (probably the contact potential of the junction) and Debye >> shielding, so some care is needed. >> >> What I found was that a lot of my favourite high-speed and >> high-linearity PDs have a buried layer of higher doping, like an APD. >> >> Boonton 72BDs are all the go. >> >> Cheers >> >> Phil Hobbs > > I like the 72Bs with the analog meter. Very retro.I like them too, but the analogue display doesn't do the stability of the meter justice. Once the 72BD is warmed up, it drifts somewhere around a femtofarad per hour in my lab. It's good enough to use for a capacitive gauge. 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
On Tue, 15 Oct 2013 13:23:58 -0400, Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:>On 10/15/2013 01:15 PM, John Larkin wrote: >> On Tue, 15 Oct 2013 13:04:01 -0400, Phil Hobbs >> <pcdhSpamMeSenseless@electrooptical.net> wrote: >> >>> On 10/15/2013 12:48 PM, George Herold wrote: >>>> On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >>>>> On 10/15/2013 01:36 AM, Jim Thompson wrote: >>>>> >>>>>> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: >>>>>> >>>>>>> >>>>>>>>> >>>>>>>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>>>>>>> would anyone *not* want to measure the power-off capacitance, and then >>>>>>>>> determine the C-V behavior? >>>>>>>> >>>>>>>> What "C-V behavior" are you referring to? >>>>>>>> >>>>>>>> ...Jim Thompson >>>> <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 >>>>> photodiodes that way, but it's more commonly used for incoming >>>>> inspection of wafers--you use a mercury or (nowadays) gallium electrode >>>>> for the top contact. >>>>> >>>> >>>> Hi Phil, Say do you have a good reference for the C-V doping density technique. >>>> >>>> I find a bit in Sze's book. I guess I can follow the references in there. >>>> >>>> George H. >>> >>> It's pretty simple. The physics is that (in the 1D approximation), in >>> order to move the edge of the depletion zone from z to z+dz, you have to >>> create a sheet of charge >>> >>> d sigma = rho dz >>> >>> and the capacitance change is >>> >>> dC = A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is >>> the dielectric constant of fully depleted silicon. >>> >>> The E field goes as the integral of the sheet charge elements >>> >>> E = 1/epsilon integral (0 to z) rho(z) dz >>> >>> and V is the line integral of the E field. >>> >>> V = integral (0 to z) E(z) dz >>> >>> So you get z from the capacitance, and then rho from the second >>> derivative of V with respect to z. Haven't got time to do the >>> derivation properly, but that's more or less how it goes. >>> >>> There are fine points having to do with where you take the origin of >>> voltage (probably the contact potential of the junction) and Debye >>> shielding, so some care is needed. >>> >>> What I found was that a lot of my favourite high-speed and >>> high-linearity PDs have a buried layer of higher doping, like an APD. >>> >>> Boonton 72BDs are all the go. >>> >>> Cheers >>> >>> Phil Hobbs >> >> I like the 72Bs with the analog meter. Very retro. > >I like them too, but the analogue display doesn't do the stability of >the meter justice. Once the 72BD is warmed up, it drifts somewhere >around a femtofarad per hour in my lab. It's good enough to use for a >capacitive gauge. > >Cheers > >Phil HobbsI've been meaning to try a parallel-plate cap as a displacement transducer. Measuring nanometers ought to be easy. -- 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 10/15/2013 01:32 PM, John Larkin wrote:> On Tue, 15 Oct 2013 13:23:58 -0400, Phil Hobbs > <pcdhSpamMeSenseless@electrooptical.net> wrote: > >> On 10/15/2013 01:15 PM, John Larkin wrote: >>> On Tue, 15 Oct 2013 13:04:01 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless@electrooptical.net> wrote: >>> >>>> On 10/15/2013 12:48 PM, George Herold wrote: >>>>> On Tuesday, October 15, 2013 11:46:30 AM UTC-4, Phil Hobbs wrote: >>>>>> On 10/15/2013 01:36 AM, Jim Thompson wrote: >>>>>> >>>>>>> On Mon, 14 Oct 2013 21:56:43 -0700, miso <miso@sushi.com> wrote: >>>>>>> >>>>>>>> >>>>>>>>>> >>>>>>>>>> I'm curious about things like ESD capacitance. Given a test setup, why >>>>>>>>>> would anyone *not* want to measure the power-off capacitance, and then >>>>>>>>>> determine the C-V behavior? >>>>>>>>> >>>>>>>>> What "C-V behavior" are you referring to? >>>>>>>>> >>>>>>>>> ...Jim Thompson >>>>> <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 >>>>>> photodiodes that way, but it's more commonly used for incoming >>>>>> inspection of wafers--you use a mercury or (nowadays) gallium electrode >>>>>> for the top contact. >>>>>> >>>>> >>>>> Hi Phil, Say do you have a good reference for the C-V doping density technique. >>>>> >>>>> I find a bit in Sze's book. I guess I can follow the references in there. >>>>> >>>>> George H. >>>> >>>> It's pretty simple. The physics is that (in the 1D approximation), in >>>> order to move the edge of the depletion zone from z to z+dz, you have to >>>> create a sheet of charge >>>> >>>> d sigma = rho dz >>>> >>>> and the capacitance change is >>>> >>>> dC = A epsilon(1/(z+dz) - 1/z) ~ -A epsilon/z**2 dz. Here epsilon is >>>> the dielectric constant of fully depleted silicon. >>>> >>>> The E field goes as the integral of the sheet charge elements >>>> >>>> E = 1/epsilon integral (0 to z) rho(z) dz >>>> >>>> and V is the line integral of the E field. >>>> >>>> V = integral (0 to z) E(z) dz >>>> >>>> So you get z from the capacitance, and then rho from the second >>>> derivative of V with respect to z. Haven't got time to do the >>>> derivation properly, but that's more or less how it goes. >>>> >>>> There are fine points having to do with where you take the origin of >>>> voltage (probably the contact potential of the junction) and Debye >>>> shielding, so some care is needed. >>>> >>>> What I found was that a lot of my favourite high-speed and >>>> high-linearity PDs have a buried layer of higher doping, like an APD. >>>> >>>> Boonton 72BDs are all the go. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> I like the 72Bs with the analog meter. Very retro. >> >> I like them too, but the analogue display doesn't do the stability of >> the meter justice. Once the 72BD is warmed up, it drifts somewhere >> around a femtofarad per hour in my lab. It's good enough to use for a >> capacitive gauge. >> >> Cheers >> >> Phil Hobbs > > > 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 -- 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
