4 ms·

Wouldn't work for all applications, tough, if I'm not mistaken, as you specifically need Silicon for imaging chips (CCD/CMOS). Or is that nonsense?

Someone 12y ago
Why would you need silicon for that? Even if it were the only process we use now (which it isn't. As a simple example, Germanium-based photo diodes do exist), materials research could conceivably produce other materials that work, too. There are even more exotic examples to think of. Eyes turn light into electricity without (AFAIK) Silicon. Maybe part of that physics/chemistry can be practically used elsewhere?
- spiritplumber 12y ago
  Germanium diodes are still made because they have a much smaller voltage drop than silicon diodes do (0.1V nominal versus 0.7V nominal). This has its uses.
- wyager 12y ago
  >Eyes turn light into electricity without (AFAIK) Silicon. Correct. A photon hits a chromophore bound to an opsin protein, and flips the chirality of the chromophore from 11-cis to all-trans, which changes the structure of the opsin protein, which starts the cascade of activity leading to sight. We could definitely use chemical detectors to take advantage of this or a similar process.
- na85 12y ago
  /nitpick: Nerve impulses are not electricity. There is a moving charge gradient which is not the same as an electric current.
gus_massa 12y ago
Theoretically you can make integrated circuit with any semiconductor, but I don't know if anyone has been brave enough to try it. The smallest integrated circuit is a diode, it has 1/2 transistors :). OK, a diode is not actually an integrated circuit, but if you can use a material to make a diode, you probably can use the same material to make an integrated circuit with enough money, time and ingenuity. Some of the diodes are made of germanium. It has a very low band gap, that is useful for "crystal radios" ( http://en.wikipedia.org/wiki/Crystal_radio#Crystal_detector http://en.wikipedia.org/wiki/Crystal_radio#Crystal_detector ). Perhaps this can be useful to make very low voltage CI, to reduce the power and heat. But perhaps there is a technical problem that I don't know. The diodes in the LED have many semiconductors. The band gap of the material is related to the color ( http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and... ). With this you could make high voltage CI (like 10V?). Perhaps it may reduce the noise ratio??? But perhaps there is a technical problem that I don't know. [kens: If you are reading this, I'd love to see a technical post about this subject.] -- Edit: According to Wikipedia, one of the first CI was made of Germanium: http://en.wikipedia.org/wiki/Integrated_circuit#Invention http://en.wikipedia.org/wiki/Integrated_circuit#Invention > Half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilby's had not. Noyce's design was made of silicon, whereas Kilby's chip was made of germanium. Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation caused by the action of a biased p–n junction (the diode) as a key concept behind the IC.
- wlievens 12y ago
  I know that, but I don't think every material has the interesting properties that Si does for image sensors, i.e. it needs to basically turn photons of the right wavelength range into electrons.
  - gus_massa 12y ago
    Sorry. I misread your comment. Other users have answered the question, but I'd like to add a little more information. http://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor http://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor > As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sensitive to blue light and to some green light, but not to yellow or red light. If you want to measure the light of all visible wavelength, you must use a semiconductor with a low band gap, for example the named in the other comments: Germanium, Silicon or Gallium Arsenide It's interesting to read the table in http://en.wikipedia.org/wiki/List_of_semiconductor_materials#Table_of_semiconductor_materials http://en.wikipedia.org/wiki/List_of_semiconductor_materials... but it's important to sort it by band gap fist, o you an compare the applications of semiconductor with a similar band gap.
    - jacquesm 12y ago
      You could use Selenium as well.
- TheLoneWolfling 12y ago
  > "Germanium differs from silicon in that the supply for germanium is limited by the availability of exploitable sources, while the supply of silicon is only limited by production capacity since silicon comes from ordinary sand or quartz. As a result, while silicon could be bought in 1998 for less than $10 per kg,[20] the price of 1 kg of germanium was then almost $800.[20]" So nearly 2 orders of magnitude price difference. In 1998 admittedly, but still. (Someone should come up with a better example for the Wikipedia article)
Sanddancer 12y ago
Other materials have been used for imagers. Gallium Arsenide in particular has been used for high speed, and high radiation, imaging circuits.
- wlievens 12y ago
  Cool, I didn't know that.
  - Create 12y ago
    venera, cray etc.
analog31 12y ago
I work with optical detectors. There are certainly other materials that can be used for imaging. There are some things going for silicon -- depending on the application of course. Notably, it's sensitive to the visible wavelength range, up into the UV, and can be turned into detectors with extremely low self-noise. It can be manufactured at a level of purity that allows for extremely low electrical leakage that would otherwise add noise. Any system of two or more elements can't reach this purity because it would require an absolutely perfect stoichiometric mixture. Large "scientific" CCD's benefit from large geometries (typ. 25 micron pixels), which probably contributes to radiation hardening. But it's hard to protect a chip from radiation without keeping it in the dark. There's also the fact that silicon has received such refinement thanks to the overall semiconductor industry.
- wlievens 12y ago
  Cool, where do you work? I work for an image sensor company (CMOS - not CCD), though I'm a pure software engineer (wafer and assembly test software among other tools) so I don't know that much of device physics, only that which I've gleaned from company-wide presentations and the such.

Someone 12y ago

Why would you need silicon for that? Even if it were the only process we use now (which it isn't. As a simple example, Germanium-based photo diodes do exist), materials research could conceivably produce other materials that work, too. There are even more exotic examples to think of. Eyes turn light into electricity without (AFAIK) Silicon. Maybe part of that physics/chemistry can be practically used elsewhere?

spiritplumber 12y ago
Germanium diodes are still made because they have a much smaller voltage drop than silicon diodes do (0.1V nominal versus 0.7V nominal). This has its uses.
wyager 12y ago
>Eyes turn light into electricity without (AFAIK) Silicon. Correct. A photon hits a chromophore bound to an opsin protein, and flips the chirality of the chromophore from 11-cis to all-trans, which changes the structure of the opsin protein, which starts the cascade of activity leading to sight. We could definitely use chemical detectors to take advantage of this or a similar process.
na85 12y ago
/nitpick: Nerve impulses are not electricity. There is a moving charge gradient which is not the same as an electric current.

gus_massa 12y ago

Theoretically you can make integrated circuit with any semiconductor, but I don't know if anyone has been brave enough to try it. The smallest integrated circuit is a diode, it has 1/2 transistors :). OK, a diode is not actually an integrated circuit, but if you can use a material to make a diode, you probably can use the same material to make an integrated circuit with enough money, time and ingenuity. Some of the diodes are made of germanium. It has a very low band gap, that is useful for "crystal radios" ( http://en.wikipedia.org/wiki/Crystal_radio#Crystal_detector http://en.wikipedia.org/wiki/Crystal_radio#Crystal_detector ). Perhaps this can be useful to make very low voltage CI, to reduce the power and heat. But perhaps there is a technical problem that I don't know. The diodes in the LED have many semiconductors. The band gap of the material is related to the color ( http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and_materials http://en.wikipedia.org/wiki/Light-emitting_diode#Colors_and... ). With this you could make high voltage CI (like 10V?). Perhaps it may reduce the noise ratio??? But perhaps there is a technical problem that I don't know. [kens: If you are reading this, I'd love to see a technical post about this subject.] -- Edit: According to Wikipedia, one of the first CI was made of Germanium: http://en.wikipedia.org/wiki/Integrated_circuit#Invention http://en.wikipedia.org/wiki/Integrated_circuit#Invention > Half a year after Kilby, Robert Noyce at Fairchild Semiconductor developed his own idea of an integrated circuit that solved many practical problems Kilby's had not. Noyce's design was made of silicon, whereas Kilby's chip was made of germanium. Noyce credited Kurt Lehovec of Sprague Electric for the principle of p–n junction isolation caused by the action of a biased p–n junction (the diode) as a key concept behind the IC.

wlievens 12y ago
I know that, but I don't think every material has the interesting properties that Si does for image sensors, i.e. it needs to basically turn photons of the right wavelength range into electrons.
- gus_massa 12y ago
  Sorry. I misread your comment. Other users have answered the question, but I'd like to add a little more information. http://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor http://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor > As a photodiode, an LED is sensitive to wavelengths equal to or shorter than the predominant wavelength it emits. For example, a green LED is sensitive to blue light and to some green light, but not to yellow or red light. If you want to measure the light of all visible wavelength, you must use a semiconductor with a low band gap, for example the named in the other comments: Germanium, Silicon or Gallium Arsenide It's interesting to read the table in http://en.wikipedia.org/wiki/List_of_semiconductor_materials#Table_of_semiconductor_materials http://en.wikipedia.org/wiki/List_of_semiconductor_materials... but it's important to sort it by band gap fist, o you an compare the applications of semiconductor with a similar band gap.
  - jacquesm 12y ago
    You could use Selenium as well.
TheLoneWolfling 12y ago
> "Germanium differs from silicon in that the supply for germanium is limited by the availability of exploitable sources, while the supply of silicon is only limited by production capacity since silicon comes from ordinary sand or quartz. As a result, while silicon could be bought in 1998 for less than $10 per kg,[20] the price of 1 kg of germanium was then almost $800.[20]" So nearly 2 orders of magnitude price difference. In 1998 admittedly, but still. (Someone should come up with a better example for the Wikipedia article)

Sanddancer 12y ago

Other materials have been used for imagers. Gallium Arsenide in particular has been used for high speed, and high radiation, imaging circuits.

wlievens 12y ago
Cool, I didn't know that.
- Create 12y ago
  venera, cray etc.

analog31 12y ago

I work with optical detectors. There are certainly other materials that can be used for imaging. There are some things going for silicon -- depending on the application of course. Notably, it's sensitive to the visible wavelength range, up into the UV, and can be turned into detectors with extremely low self-noise. It can be manufactured at a level of purity that allows for extremely low electrical leakage that would otherwise add noise. Any system of two or more elements can't reach this purity because it would require an absolutely perfect stoichiometric mixture. Large "scientific" CCD's benefit from large geometries (typ. 25 micron pixels), which probably contributes to radiation hardening. But it's hard to protect a chip from radiation without keeping it in the dark. There's also the fact that silicon has received such refinement thanks to the overall semiconductor industry.

wlievens 12y ago
Cool, where do you work? I work for an image sensor company (CMOS - not CCD), though I'm a pure software engineer (wafer and assembly test software among other tools) so I don't know that much of device physics, only that which I've gleaned from company-wide presentations and the such.