ISIS Diodes

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New for April 2020. ISIS diodes are yet another historical artifact of microwave engineering, but they were how your parents made watts of solid-state power at millimeterwave frequencies. ISIS is still a pretty decent tool in the high-power toolbox that you should be aware of, as it provides high efficiency multiplication of high-power signals.

ISIS stands for integrated series IMPATT structures, an acronym within an acronym. The ISIS diode was first developed by M/A-COM in Massachusetts in 1987:

M. E. Hines, P. W. Staecker, F. Occhiuti and J. F. Cushman, "The ISIS Multi-Junction Varactor as a Pulsed Millimeter Wave Harmonic Generator," 1987 17th European Microwave Conference, Rome, Italy, 1987, pp. 693-697.

Engineers in the past could be described as a band of frustrated men... It is probably not a coincidence that they named this little bit of epitaxial magic after a Greek Godess. Perhaps the name was coined during an after-hours trip to the Athenian Corner, in Lowell MA which opened in 1974, and still features live entertainment. Today, the name ISIS has been ruined by peverts in the middle east, much the way the brand name "Ayds" was torched during the HIV crisis of the 1980s.

Athenian Corner in Lowell MA, where you can meet modern ISIS

MACOM used to make diodes in a large complex on South Avenue in Burlington MA.  It was demolished to make room for shopping (even though there is a huge shopping mall is nearby), a theater, restaurants and a hotel. Microwave Device Technology (MDT) bought out MACOM's diode business in year 2000. MDT was founded in 1988 by  ex-M/A-COM employee T B Ramachandran, who died in 2013. In 2007, MDT became part of Microsemi for $7.8M in cash.  Microsemi was acquired recently by Microchip Corp. 

Here's a report prepared for Naval Research Labs (NRL) titled "X-BAND GAAS ISIS IMPATTs", from July 1985, by Rovindra Dat and Murthy Ayyagari, at M/A-COM. It's released to the public on DTIC.

Here are some descriptions of ISIS in a Google book you can sample:

Epi stack

ISIS diodes typically come in two and three stacks.  Below is a two-stack epi:

  • (top)
  • P+
  • N
  • N+
  • P+
  • N
  • N+
  • Substrate
  • (bottom)


Below, we copied a piece of an old MDT catalog to give you some performance metrics on ISIS diodes:

ISIS multiplier varactors (see the ISIS diode schematic) are fabricated by epitaxially stacking the P-N junctions in Gallium Arsenide to obtain high powers in millimeterwave frequencies. The MIV series of ISIS multiplier diodes has been especially designed to have the highest cut-off frequency to produce very low conversion loss when used in appropriately designed circuits. MDT offers 2 and 3 stacked devices to produce high CW powers in U and W bands. Typically, CW powers of up to 3 W at 44 GHz (conversion loss >3 dB) and 1 W in W band (conversion loss >9 dB) are realizable with single devices. These diodes are offered in a very low parasitic (>10 fF) well heat-sunk M29 package and in other standard microwave packages.

Tony Bonly

This seems like an extension of an urban legend (which could be based on real circumstances, BTW), but we heard it from someone that used to work for T B.  There are many instances of people that don't have full names, just letters. This seems particularly true for people in India.

T B Ramachandron, founder of ADT, was at the Massachusetts Registry of Motor Vehicles, getting a drivers' license. The clerk asks for his name.  

"T B", he responded.

"No, those are your initials, what is your full name?" said the clerk. "I need to know what to put on your drivers' license."

"T only, B only" responded T B.

"That will work" said the clerk.

When T B picked up his license, his name was Tony Bonly Ramachandron. We are pretty sure the source of this information prefers to remain anonymous, so don't ask.


Author : Unknown Editor