Doubt regarding silicon waffers and silicon diodes

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Hi,
basically i am confused about the characteristricts of silicon diodes and waffers. As i know the VI @ CV characterstricts of the diode. But i tested the same characterstricts with silicon waffers which behaves perfectly same as like diodes. Mainly i need to know about the difference between theese two, If both are same why can't we use small peice in waffers in the place diode in diode operations. i want help towards differences between the two. As accoding to my lab instructor they both are same but he is new to that lab. So, i am bit not agree.
and more on .....

we wached VI and CV characetsticts of small silicon detector from silicon waffer. that charterstics are equal to the diode charcerstics. But i have doubt abot some questions in the process.

1)What is important to think about in the physical environment to get an accurate measurement?
How large is the leakage current at full depletion? What is full depletion? Why is it important to have a small leakage current?


could any one give suggestions for above?....
 

Answers and Replies

  • #2
berkeman
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Hi,
basically i am confused about the characteristricts of silicon diodes and waffers. As i know the VI @ CV characterstricts of the diode. But i tested the same characterstricts with silicon waffers which behaves perfectly same as like diodes. Mainly i need to know about the difference between theese two, If both are same why can't we use small peice in waffers in the place diode in diode operations. i want help towards differences between the two. As accoding to my lab instructor they both are same but he is new to that lab. So, i am bit not agree.
and more on .....

we wached VI and CV characetsticts of small silicon detector from silicon waffer. that charterstics are equal to the diode charcerstics. But i have doubt abot some questions in the process.

1)What is important to think about in the physical environment to get an accurate measurement?
How large is the leakage current at full depletion? What is full depletion? Why is it important to have a small leakage current?


could any one give suggestions for above?....
That is indeed how many diodes and transistors are made -- in wafer form, and then cut up into individual parts. Just like larger ICs, which are composed of many diodes and transistors.

http://en.wikipedia.org/wiki/Integrated_circuit

.
 
  • #3
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As you said waffer is inbuilt of many diodes or what ever characterstic it has but we just observe the small chip(one part of silicon waffer) VI and CV characterstics with HPVEE(which is made from our univ for mesuring these characterstics). that both characterstics are samae as diode. i am little bit confused abt how they have same characterstics as diode and above questions abt physical environment and full depletion.

i wnat explanation about those questions..
 
  • #4
berkeman
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As you said waffer is inbuilt of many diodes or what ever characterstic it has but we just observe the small chip(one part of silicon waffer) VI and CV characterstics with HPVEE(which is made from our univ for mesuring these characterstics). that both characterstics are samae as diode. i am little bit confused abt how they have same characterstics as diode and above questions abt physical environment and full depletion.

i wnat explanation about those questions..
Sorry if we are not connecting well on the question and answer.

What IC mask geometry size do the diodes and transistors have on the wafer you are probing? 180nm? 90nm? Other?

And what separate packaged diodes are you comparing them to? 1N4148? BAV99? 1N5914?

Why is it that getting similar characteristics when probing a loose diode and probing a diode still on its wafer surprises you?
 
  • #5
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Hi,
basically i am confused about the characteristricts of silicon diodes and waffers. As i know the VI @ CV characterstricts of the diode. But i tested the same characterstricts with silicon waffers which behaves perfectly same as like diodes.

How did you make your contacts? Are you sure they are ohmic? If you don't prepare them correctly, you will have a Schottky barrier.
 
  • #6
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How did you make your contacts? Are you sure they are ohmic? If you don't prepare them correctly, you will have a Schottky barrier.
these all examinations has done in clean room where the waffers are prepared. we did not even touch the waffers with hand or other physical coordination. just we taken a sample(a small part in waffer like squre shape and size that we used about TAB button in laptops)and placed in between one programmed mission called HPVEE(made from our univ) and then we run the program then it plot the VI and CV characteristics with some iput parameters.
for that lab they just done all the things infront of us and at last just we copied the results means that characteristics of VI and CV.

if your uncomfortable with these unknown topics please make me clear in the direction of questions what i written on first message about full depletion and physical environment(that day in lab we switched off all the lights in lab and measured these characteristics)
 
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  • #7
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doubt in fabrication

Why is silicon dioxide so important in fabrication of silicon detectors?
 
  • #8
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where the waffers are prepared.
What kind of wafers are you talking about? Bare or processed?

If it is a bare wafer, you must deposit some kind of metal and properly anneal it to get an ohmic contact. The type of metal depends on the semiconductor material. You can't just press down a probe on the surface and expect an ohmic contact.

If it is a processed wafer, what has been fabricated? If it is a diode, then I will echo berkeman's response:
Why is it that getting similar characteristics when probing a loose diode and probing a diode still on its wafer surprises you?
As for your other questions:
1)What is important to think about in the physical environment to get an accurate measurement?
Make good contacts. In the dark is a good idea. Remove noise sources. Check your equipment's accuracy using a similar standard diode and its datasheet.

How large is the leakage current at full depletion?
Ideally, zero. There is no universal value for the non-ideal case. It depends on the device and many parameters.

What is full depletion?
In what context/device? It means all carriers have been depleted/removed (ideally carrier concentration = 0)

Why is it important to have a small leakage current?
You don't want parasitic paths.
 
  • #9
132
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What kind of wafers are you talking about? Bare or processed?

If it is a bare wafer, you must deposit some kind of metal and properly anneal it to get an ohmic contact. The type of metal depends on the semiconductor material. You can't just press down a probe on the surface and expect an ohmic contact.

If it is a processed wafer, what has been fabricated? If it is a diode, then I will echo berkeman's response:


As for your other questions:

Make good contacts. In the dark is a good idea. Remove noise sources. Check your equipment's accuracy using a similar standard diode and its datasheet.


Ideally, zero. There is no universal value for the non-ideal case. It depends on the device and many parameters.


In what context/device? It means all carriers have been depleted/removed (ideally carrier concentration = 0)


You don't want parasitic paths.
thank you so much...and we used processed waffers and can you help me about why the that silicon waffer is giving VI characterstics as diode and what internally waffer got and how the p-type and n-type materials form in waffer..
 
  • #10
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thank you so much...and we used processed waffers and can you help me about why the that silicon waffer is giving VI characterstics as diode and what internally waffer got and how the p-type and n-type materials form in waffer..
It's hard to tell without knowing what was processed, but my guess is that it looks like a diode because it is a diode (pn junction). Any neighboring p and n regions will have a diode-like IV curve unless they are isolated by etching. If you measure the IV curve between the base and collector or emitter of a bipolar transistor, you will get a diode-like reading.

There are many ways to make p or n regions:
1) The substrate (wafer) itself can be made p or n simply by adding dopants to the melt from which the boule is pulled
2) Ion implantation is the most common way
3) Epi growth can also be used to make p or n-type layers

Wikipedia has a lot of information about semiconductor processing.
 
  • #11
berkeman
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Why is silicon dioxide so important in fabrication of silicon detectors?
rama, we should not be doing your lab report for you. We expect you to do the bulk of the work on your schoolwork. If there is something that is confusing you, we can try to help point you to resources where you should be able to answer your questions.

So what do you think about this question you've asked? Why is Silicon Dioxide used in semiconductor fabrication?
 
  • #12
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What kind of wafers are you talking about? Bare or processed?

If it is a bare wafer, you must deposit some kind of metal and properly anneal it to get an ohmic contact. The type of metal depends on the semiconductor material. You can't just press down a probe on the surface and expect an ohmic contact.

If it is a processed wafer, what has been fabricated? If it is a diode, then I will echo berkeman's response:


As for your other questions:

Make good contacts. In the dark is a good idea. Remove noise sources. Check your equipment's accuracy using a similar standard diode and its datasheet.


Ideally, zero. There is no universal value for the non-ideal case. It depends on the device and many parameters.


In what context/device? It means all carriers have been depleted/removed (ideally carrier concentration = 0)


You don't want parasitic paths.


can any one explain briefly about the last question that why its important to have a leakage current.
 
  • #13
berkeman
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[/COLOR]

can any one explain briefly about the last question that why its important to have a leakage current.
It's not. Leakage current is bad.
 

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