Would this be more interesting if it were Ramtron's IP:
Features
Rohm Develops Non-Volatile Register; Slashes Dissipation
Nikkei Electronics Asia -- August 2008
Rohm Co Ltd of Japan has developed a technology that makes possible non-volatile registers, latches and other elements used in the digital circuits inside integrated circuits (IC). In most cases, these elements are composed of flip-flops or similar structures, meaning that stored data is lost when the power supply is shut off. The non-volatile register developed by Rohm adds a ferroelectric capacitor to a standard register, thereby retaining stored data even when the power is off. This means that power supply to specific circuit blocks, or even the entire IC, can be shut off when in stand-by, significantly reducing leakage current and slashing total IC dissipation.
To confirm the efficacy of the technology, researchers prototyped an IC integrating the Z80 8-bit central processing unit (CPU) core using the new non-volatile register. The entire CPU core was operated intermittently, for only 4ms of the total 14ms cycle, with power cut off for the remaining 10ms, to achieve a reduction in dissipation of about 70%. The company plans to develop an application-specific IC (ASIC) library using the non-volatile register and begin booking orders from equipment manufacturers in about 2009, with an eye on volume production.
In addition to standard complementary metal-oxide semiconductor (CMOS) manufacturing processes, the new register also requires a process to form the ferroelectric capacitor. According to Hidemi Takasu, member of the board, director of Rohm, however, "The ferroelectric capacitor is stacked on top of the standard CMOS transistor.
The metallization layer requires only minimal processing, and we believe it will have very little impact on cost." Ferroelectric random-access memory (FeRAM) non-volatile storage, used as main memory for microcontrollers, system ICs, etc, utilizes ferroelectric capacitors formed using the same technology. The prototyped chip was manufactured with 350nm-generation technology, but the firm plans to construct a 130nm-generation volume production line.
CMOS-Like Performance
The outstanding feature of the new register is that it is not only non-volatile, but delivers the same speed and data retention reliability as standard CMOS technology registers. A standard CMOS register has a ferroelectric capacitor formed in parallel with it (see Fig). The capacitor is connected via a buffer and switch. When the standard register operates logically within the pipeline, it is electrically isolated by the ferroelectric capacitor, so operating speed is the same as the CMOS register.
Rohm has been working on non-volatile registers for at least six years, and under conventional technology used a ferroelectric capacitor connected to the register output signal line. This meant that every time the register flipped logically, voltage was input to the ferroelectric capacitor. The resulting parasitic capacitance degraded register operating speed, shortened ferroelectric capacitor write life and had other adverse effects.
In addition, the ferroelectric capacitor was driven on the standard register signal line, and every time the ferroelectric capacitor was written to, it could cause the register to flip, corrupting data and degrading the reliability of logic circuit computation. Improvements in circuit technology, such as the addition of buffers, switches, etc, resolved these problems, maturing the technology to the level needed for commercial use.
Power Supply Control
The biggest problem with the new non-volatile register is determining what circuit level to cut power off in. From the standpoint of minimizing standby dissipation, the most effective approach would be to detect which registers are likely to be unused for a while, and cut off the supply to those registers individually. Given the enormous number of registers found in ICs, though, a system-wide approach would be essential.
At present, the firm is still researching technologies that could assist in implementing this system-wide evaluation, for which reason the supply to the entire CPU core was shut off in this prototype. Rohm plans to implement power supply control in block units, such as decoder or arithmetic logic unit (ALU), when launching volume production a year from now.
by Tomonori Shindo
Nikkei Electronics
techon.nikkeibp.co.jp
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