ESFET

[doanster]

so what exactly is an ES field effect transistor?

 

[pm]

I've never heard of an "ESFET" - Google turns up a sensor. Are you sure you don't mean "MESFET" which are more commonly used devices?

 

[TuxDave]

Originally posted by: pm
I've never heard of an "ESFET" - Google turns up a sensor. Are you sure you don't mean "MESFET" which are more commonly used devices?

MESFET was the first thing that came to my mind too. However, I was so terrible with device physics that I couldn't tell you how having a metal gate makes it great. 😛

 

[RaynorWolfcastle]

Originally posted by: TuxDave

Originally posted by: pm
I've never heard of an "ESFET" - Google turns up a sensor. Are you sure you don't mean "MESFET" which are more commonly used devices?

MESFET was the first thing that came to my mind too. However, I was so terrible with device physics that I couldn't tell you how having a metal gate makes it great. 😛

I think that the idea is to use the increased carrier mobility of GaAs and other III-V semiconductors. IIRC the reasons they use MESFETs rather than MOSFETs in III-V semis is that there's no easy way to put an insulator like silicon dioxide for gate insulation.

I'm not absolutely sure about this, but I think that HEMTs and PHEMTs are supposed to improve on the MESFET structure to allow for even faster devices (several hundred GHz operation)

 

[MrDudeMan]

Originally posted by: RaynorWolfcastle

Originally posted by: TuxDave

Originally posted by: pm
I've never heard of an "ESFET" - Google turns up a sensor. Are you sure you don't mean "MESFET" which are more commonly used devices?

MESFET was the first thing that came to my mind too. However, I was so terrible with device physics that I couldn't tell you how having a metal gate makes it great. 😛

I think that the idea is to use the increased carrier mobility of GaAs and other III-V semiconductors. IIRC the reasons they use MESFETs rather than MOSFETs in III-V semis is that there's no easy way to put an insulator like silicon dioxide for gate insulation.

I'm not absolutely sure about this, but I think that HEMTs and PHEMTs are supposed to improve on the MESFET structure to allow for even faster devices (several hundred GHz operation)

i recall reading something like that in a book a few weeks ago. im not totally sure either, but that sounds right.

also, several hundred GHz? wow.

 

[RaynorWolfcastle]

Originally posted by: Bigsm00th

Originally posted by: RaynorWolfcastle
I think that the idea is to use the increased carrier mobility of GaAs and other III-V semiconductors. IIRC the reasons they use MESFETs rather than MOSFETs in III-V semis is that there's no easy way to put an insulator like silicon dioxide for gate insulation.

I'm not absolutely sure about this, but I think that HEMTs and PHEMTs are supposed to improve on the MESFET structure to allow for even faster devices (several hundred GHz operation)

i recall reading something like that in a book a few weeks ago. im not totally sure either, but that sounds right.

also, several hundred GHz? wow.

I should clear up that I meant that f_max is several hundred GHz, actual operating frequency is likely to be more in the range of 10s of GHz. GaAs and other III-V compounds are generally not used for logic, they are mainly used in the analog front-end of a transciever (optical or wireless).

 

[MrDudeMan]

Originally posted by: RaynorWolfcastle

Originally posted by: Bigsm00th

Originally posted by: RaynorWolfcastle
I think that the idea is to use the increased carrier mobility of GaAs and other III-V semiconductors. IIRC the reasons they use MESFETs rather than MOSFETs in III-V semis is that there's no easy way to put an insulator like silicon dioxide for gate insulation.

I'm not absolutely sure about this, but I think that HEMTs and PHEMTs are supposed to improve on the MESFET structure to allow for even faster devices (several hundred GHz operation)

i recall reading something like that in a book a few weeks ago. im not totally sure either, but that sounds right.

also, several hundred GHz? wow.

I should clear up that I meant that f_max is several hundred GHz, actual operating frequency is likely to be more in the range of 10s of GHz. GaAs and other III-V compounds are generally not used for logic, they are mainly used in the analog front-end of a transciever (optical or wireless).

i thought GaAs was actually semi-common in semiconductors, especially transistors. i know that has been mentioned in class, but maybe i am confused or misunderstood.

 

[RaynorWolfcastle]

Originally posted by: Bigsm00th
i thought GaAs was actually semi-common in semiconductors, especially transistors. i know that has been mentioned in class, but maybe i am confused or misunderstood.

Truth be told, at the moment CMOS is pretty much the only mainstream semiconductor technology. Even RFICs that used to be reserved to BJTs, SiGe, and GaAs are being taken over as CMOS die shrinks have increasingly higher f_t. To give you an idea, 90nm CMOS can (though it is challenging) be used for most RFIC applications such as GSM transceivers, WiFi front-ends, etc.

The only place that CMOS still hasn't pervaded is the 5 GHz+ range, that is high-RF, microwave, and millimeter wave applications. UWB chips (which are supposed to work up to 10GHz) are still near impossible on CMOS. Chips for OC-768 (40 Gbps) are impossible in CMOS AFAIK and are done in GaAs.

CMOS has become so dominant for mainly three reasons: low power-consumption, massive integrability, low cost. People tend to think that CMOS is "fast", but the truth is that Si BJTs, SiGe, and GaAs are all faster. Optoelectronics are actually nearly always done in GaAs because it is very fast and has good optical properties.

Anyhow, I'm rambling now but if you want more details, feel free to PM me 🙂

 

[sdifox]

On a slightly related slant, whatever happened to photonic computers? They were in vogue, oh, 15 years ago, but last I heard was they were hacing problems with switches not being fast enough.