MEMS Version of Intel 4004 Chip Could be Made to Prove Nanomechanical Computer Designs

Ralph Merkle, Robert Freitas and collaborators have shown that using only links and rotary joints a Turing-complete computational system can be created. A version of this design could be built using existing and popular 2 micron MEMS technology to make a chip that would equal the 4-bit Intel 4004 CPU. The Intel 4004 came out in 1971 and was the first commercially available microprocessor by Intel.

Universal combinatorial logic has been demonstrated with the design of a NAND gate, while sequential logic, mimicking electronic flip-flops and sufficient to create memory has been demonstrated using cells combined into shift registers.

Above – Part of a molecular mechanical logic gate. This molecular machine would have 120695 atoms, 87595 carbon and 33100 hydrogen, and occupies a volume of about 27 nm × 32 nm × 7 nm.

The design approach is far simpler than any other mechanical Turing-complete design. The design avoids almost all sliding friction so the design has the potential to be more power efficient than any previous design. In fact, simulations suggest that molecular-scale implementations of the described system would be far more power efficient than conventional electronic computers.

Silicon-based electronic computers are everywhere and are cheap and powerful so why would we want nanomechanical computers? Many research groups are currently investigating mechanical, electromechanical, and biochemical alternatives to conventional semiconductor computer architectures because of their unique potential
advantages. Mechanical systems can withstand much higher temperature and radiation exposure than their electronic counterparts, and hence may be useful in certain niche applications.

MEMS Version is Possible

Flexure joints provide an alternative implementation with similar general performance to pivots. Flexures have the advantage that in many cases, particularly with MEMS, they are easier to fabricate and often more reliable than fully functional pivot joints.

A systematic method of design allows all necessary locks, balances, bell cranks, support links, and transmission links to be implemented in only two layers of material.

What could be possible with conventional MEMS technology?

The minimum feature size of the popular Multi-User MEMS Processes (MUMPs) commercial program is two microns. If the flexures are two microns in width then a pair of transistors would cover an area of 640 × 1070 microns. A silicon die 2.8 cm square could contain the mechanical equivalent to 2,200 transistors, which is the transistor count in the 4-bit Intel 4004 CPU.

Nanomechanical Version Would Be 100 Billion Times More Energy Efficient Than Todays Computers

A nano-mechanical computer could be 100 billions of times more energy efficient than current computers. A previous version of the nanomechanical design calculated potential efficiency. The nanomechanical computer is well-suited for implementing physically reversible logic gates. Reversible logic gates are one alternative technology that can, in principle, sidestep fundamental limitations of complementary metal-oxide-semiconductor (CMOS) transistors, and thus facilitate computers that operate with vastly reduced energy dissipation.

They remove the need for gears, clutches, switches, springs and make the design easier to build. Existing designs for mechanical computing can be vastly improved upon in terms of the number of parts required to implement a complete computational system. Only two types of parts are required: Links, and rotary joints. Links are simply stiff, beam-like structures. Rotary joints are joints that allow rotational movement in a single plane.

Simple logic and conditional routing can be accomplished using only links and rotary joints, which are solidly connected at all times. No gears, clutches, switches, springs, or any other mechanisms are required. An actual system does not require linear slides. Any traditional 2-input logic gate, including AND, NAND, NOR, NOT, OR, XNOR and XOR, can be created directly from the appropriate combination of locks and balances. Reversible gates can also be created using only links and rotary joints, and a Fredkin gate is also demonstrated.

Universal combinatorial logic and sequential logic together are known to be enough to make a general-purpose (Turing-complete) computational system. Subject to practical limits of time and memory (as in any computer), such a system can compute anything that can be computed.

Reversible Computing

A mechanical computer designed as described herein has the potential to provide 1 trillion GFLOPS/Watt, over 100 billion times more efficient than conventional “green” supercomputers, which currently provide about 18 GFLOPS/Watt.

The Landauer Limit of 4 x 10^-21 J per logical operation is quite large compared to the energy lost to friction via a NAND gate of the link- and rotary-joint style (3.9 x 10^-26 J per logical operation). It makes little sense to have such an efficient mechanism, but to then operate it in such a manner that power losses due to bit erasure reduce its effective efficiency by several orders of magnitude.

Reversible computing is a well-known way to circumvent the Landauer Limit. Using reversible computing schemes, bits are stored, even if technically no longer needed to produce the final output, so that the penalty associated with bit erasure is not incurred. It would be trivial to modify the described NAND gate to be reversible.

Arxiv – Mechanical Computing Systems Using Only Links and Rotary Joints

SOURCES – Arxiv, Ralph Merkle, Robert Freitas
Written By Brian Wang.