What property of a MOSFET products gain? - Page 1
Forum section: electronics / beginners

author: steamedhams
author_rank: Regular Contributor
timestamp: November 19, 2021, 04:49:26 pm
content: What is it about a MOSFET makes gain possible??https://electronics.stackexchange.com/questions/377783/mosfet-voltage-gain-in-common-source-configurationOn a physics level... I get the formula but not the physics.I work with loads of semiconductor engineers and no one seems to be able to give me a straight answer.

author: tszaboo
author_rank: Super Contributor
timestamp: November 19, 2021, 04:52:29 pm
content: Nothing inside the FET. It's a voltage to current converter. The voltage on the external resistor creates the gain.

author: TimFox
author_rank: Super Contributor
timestamp: November 19, 2021, 05:37:23 pm
content: The fundamental property of an active device used in an amplifier is that a small signal applied to the input (e.g., voltage at grid of a vacuum tube or gate of a MOSFET or JFET, or voltage and current at base of BJT) changes the larger signal at the output (usually current at plate of tube, collector of BJT, or drain of FET) that can change the power into a load (e.g., drain resistor or load coupled through transformer to output terminal of device).In the case of JFETs or MOSFETs, the gate-source voltage modulates the effective conducting width of the channel between drain and source, so that the drain current changes.

author: David Hess
author_rank: Super Contributor
timestamp: November 19, 2021, 11:39:29 pm
content: The gate voltage reverses the effect of the doping in the channel on the opposite side of the gate insulator, changing its type from N to P or P to N. Bipolar transistors do the same thing by injecting minority carriers.

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 20, 2021, 08:11:27 am
content: I think getting a straight anwer here is hard, because the computing industry is a complete sham, they dont want you to work out how easy it is to fab your own transistors, because if everyone knew the price of computers would plummet.

author: TimFox
author_rank: Super Contributor
timestamp: November 20, 2021, 03:12:11 pm
content: Have you ever read a newspaper article about the cost of new integrated circuit fabrication factories?Back in the day, some advanced amateurs actually built their own vacuum tubes (often by remanufacturing older units), and in the 1950s some even built their own point-contact bipolar transistors.Do you have any evidence that anyone, ever, built their own MOSFET at home? What was the cost with respect to purchasing one at DigiKey?

author: george.b
author_rank: Frequent Contributor
timestamp: November 20, 2021, 04:00:19 pm
content: Quote from: TimFox on November 20, 2021, 03:12:11 pm

author: TimFox
author_rank: Super Contributor
timestamp: November 20, 2021, 05:17:54 pm
content: Very interesting. I didn't view the video: how much did that effort cost to make one MOSFET, and what were its properties and size of the actual device?The physics of semiconductor devices is well covered in technical books. The original poster had read such physical descriptions, and was inquiring as to how such a device functioned as an amplifier.

author: Monkeh
author_rank: Super Contributor
timestamp: November 20, 2021, 05:22:32 pm
content: Quote from: Capernicus on November 20, 2021, 08:11:27 amSure, it is pretty easy. You just have to make a few trillion of them. And they all have to work perfectly.

author: David Hess
author_rank: Super Contributor
timestamp: November 20, 2021, 08:18:39 pm
content: Quote from: TimFox on November 20, 2021, 05:17:54 pmIt worked, but performance was marginal. Bipolar transistors are easier to manufacturer. I suspect he could make some money making tunnel diodes which are also relatively easy to manufacturer if he could get the parts for the cases.

author: Simon
author_rank: Unknown
timestamp: November 20, 2021, 08:41:21 pm
content: Quote from: Capernicus on November 20, 2021, 08:11:27 amwhat has this forum got to do with any sector of the industry? if it's so easy why are you not doing it and raking it in?

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 22, 2021, 02:52:21 am
content: I bet he can make heaps of them, Me myself I dont even need em just use caps for logic is fine for me. and everyone knows how easy caps are to make below a picofarad.

author: tooki
author_rank: Super Contributor
timestamp: November 22, 2021, 03:44:52 am
content: Quote from: Simon on November 20, 2021, 08:41:21 pmCan we just ban that troll once and for all? His “contributions” only add negative value to the forums…

author: Capernicus
author_rank: Frequent Contributor
timestamp: November 22, 2021, 06:11:36 am
content: what am i an informer? Does everything I say make too much sense and said too clear and concisely?Does it get cheesy and embaressing when everyone knows how to do it?

author: tooki
author_rank: Super Contributor
timestamp: November 22, 2021, 05:05:56 pm
content: Quote from: Capernicus on November 22, 2021, 06:11:36 amNo, it doesn’t make sense. You’re just either a troll, or quite an extreme case of Dunning-Kruger.If you knew the first thing about semiconductor manufacturing you’d know that aside from involving tons of dangerous chemicals and processes, it’s unbelievably sensitive to contamination.When Fairchild started making transistors commercially, their yields fluctuated dramatically, and it took them a while to figure out that yields dropped when (among other things) the farmers miles away sprayed their crops, or when an employee failed to wash his hands after peeing. (Note that this was despite handling the wafers with gloves!)Meanwhile, cutting edge ICs (like the ones used in smartphones) use features so fine that they can only be made using extreme UV light (i.e. nearly x-rays). It takes a multibillion-dollar factory to make those things. You’re not going to replicate that at home, or even in a lab. It requires the ultra-specialized equipment of a new fab.Can you make a single giant transistor yourself? Sure, if you’ve got the equipment and don’t mind dealing with chemicals that can eat your bones from the inside out.But making anything beyond a “just to show it’s possible” lab experiment? Not a snowball’s chance in hell.

author: BrianHG
author_rank: Super Contributor
timestamp: November 23, 2021, 09:26:21 am
content: This is the most complex home made IC I have seen yet:

author: tooki
author_rank: Super Contributor
timestamp: November 23, 2021, 06:22:11 pm
content: Yup! Just 6 orders of magnitude to go and we’ll all be making chips at home! 🤣

author: David Hess
author_rank: Super Contributor
timestamp: November 24, 2021, 09:55:35 pm
content: There are plenty of useful ICs and other semiconductors which are made with much lower resolution lithography. There is no requirement for a garage lab to produce anything close to the highest transistor density.Other processing factors other than resolution of the lithography are more important.

author: Simon
author_rank: Unknown
timestamp: November 25, 2021, 07:04:20 am
content: OK, so what parts can you offer us in these times of shortage?