IIT Bombay researchers have developed a “memory technology” that can, in principle, revolutionise Indian industry and the many applications that need semiconductor chips, such as in the defence sector, automobiles and future aspirations in cell phone manufacturing.

One-time Programmable Memory

• Hard disks, flash memory, etc, are examples of memory technology.
• There is also another form of memory called the one-time programmable memory (OTP) where the memory is written once, stored for a lifetime, and retrieved and used many times.
• This finds varied uses, one of which is in correcting faulty chips that have been mass produced for specific applications.

Its utility

• For instance, think of a chip that helps read off the temperature.
• Due to a manufacturing defect, the chip may read 100 degree Celsius as 101 degree Celsius.
• This “offset” of 1 degree may be corrected by storing the error correction parameter in the OTP memory.
• This is done uniquely for each chip and once stored, the memory corrects the chip’s output for its lifetime.
• OTP memories are also used for other purposes, mainly three: chip identity, secure information storage and chip calibration for error correction.

How does it work?

• To store the correction value, the researchers used eight memory cells, each of which would store one “bit” (that is a value of zero or one).
• Each of the memory cells consist of an ultrathin silicon dioxide layer which is 10-15 atomic layers thick.
• This is deposited uniformly over a dinner plate–sized eight-inch silicon wafer to form millions of nanoscale capacitors.
• The pristine silicon dioxide layer is insulating, passing a very low current [which in digital electronics is read as a “0”].
• A nanoscale lightning is generated of 3.3 volts to blow the capacitor, leading to a short circuit that produced high current [this is a “1”].
• Thus, the OTP memory remembers either the “0” state or “1” state through its lifetime.

Benefits offered

1. Low voltage reads
2. Small memory footprint
3. High security
4. Flexibility ; Portability and scalability
5. High reliability

• The group has successfully demonstrated CMOS 180-nanometre–based, production-ready, eight-bit memory technology.
• These include successful operation between minus 40 degrees C to 125 degrees C and reliability to ensure excess of 95% yield on eight-bit memories.

Significance

• A large fraction of manufactured chips may need to be discarded for faults that can be corrected using this technology.
• This technology is the first indigenous semiconductor memory technology adoption to manufacturing at 180-nanometre node.
• Thus, this is a major national milestone for semiconductor innovation.