Modern cryptography relies on algorithmic one-way functions—numerical functions which are easy to compute but very difficult to invert. This dissertation introduces physical one-way functions and physical one-way hash functions as primitives for physical analogs of cryptosystems. 
Physical one-way functions are defined with respect to a physical probe and physical system in some unknown state. A function is called a physical one-way function if (a) there exists a deterministic physical interaction between the probe and the system which produces an output in constant time; (b) inverting the function using either computational or physical means is difficult; (c) simulating the physical interaction is computationally demanding and (d) the physical system is easy to make but difficult to clone. 
Physical one-way hash functions produce fixed-length output regardless of the size of the input. These hash functions can be obtained by sampling the output of physical one-way functions. For the system described below, it is shown that there is a strong correspondence between the properties of physical one-way hash functions and their algorithmic counterparts. In particular, it is demonstrated that they are collision-resistant and that they exhibit the avalanche effect, i.e., a small change in the physical system causes a large change in the hash value. 
An inexpensive prototype authentication system based on physical one-way hash functions is designed, implemented, and analyzed. The prototype uses a disordered three-dimensional microstructure as the underlying physical system and coherent radiation as the probe. It is shown that the output of the interaction between the physical system and the probe can be used to robustly derive a unique tamper-resistant identifier at a very low cost per bit. The explicit use of three-dimensional structures marks a departure from prior efforts. Two protocols, including a one-time pad protocol, that illustrate the utility of these hash functions are presented and potential attacks on the authentication system are considered. 
Finally, the concept of fabrication complexity is introduced as a way of quantifying the difficulty of materially cloning physical systems with arbitrary internal states. Fabrication complexity is discussed in the context of an idealized machine—a Universal Turing Machine augmented with a fabrication head—which transforms algorithmically minimal descriptions of physical systems into the systems themselves. (Copies available exclusively from MIT Libraries, Rm. 14-0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)

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Physical one-way functions

An electrostatically deflectable beam spatial light modulator with the beams (30), address electrodes (42, 46), and landing electrodes (40, 41) to provide soft-landing of the beams on the landing electrodes (40, 41) which gives uniform large-angle deflection plus high reliability.

Spatial light modulator and method

A Three Dimensional Structure (3DS) Memory (100) allows for physical separation of the memory circuits (103) and the control logic circuit (101) onto different layers (103) such that each layer may be separately optimized. One control logic circuit (101) suffices for several memory circuits (103), reducing cost. Fabrication of 3DS memory (100) involves thinning of the memory circuit (103) to less than 50 microns in thickness and bonding the circuit to a circuit stack while still in wafer substrate form. Fine-grain high density inter-layer vertical bus connections (105) are used. The 3DS memory (100) manufacturing method enables several performance and physical size efficiencies, and is implemented with established semiconductor processing techniques.

Three dimensional structure memory

The combination of decreasing feature sizes and increasing chip sizes is leading to a communication crisis in the area of VLSI circuits and systems. It is anticipated that the speeds of MOS circuits will soon be limited by interconnection delays, rather than gate delays. This paper investigates the possibility of applying optical and electrooptical technologies to such interconnection problems. The origins of the communication crisis are discussed. Those aspects of electrooptic technology that are applicable to the generation, routing, and detection of light at the level of chips and boards are reviewed. Algorithmic implications of interconnections are discussed, with emphasis on the definition of a hierarchy of interconnection problems from the signal-processing area having an increasing level of complexity. One potential application of optical interconnections is to the problem of clock distribution, for which a single signal must be routed to many parts of a chip or board. More complex is the problem of supplying data interconnections via optical technology. Areas in need of future research are identified.

Optical interconnections for VLSI systems

Along with extensive research on the three-dimensional (3D) printing of polymers and metals, 3D printing of ceramics is now the latest trend to come under the spotlight. The ability to fabricate ceramic components of arbitrarily complex shapes has been extremely challenging without 3D printing. This review focuses on the latest advances in the 3D printing of ceramics and presents the historical origins and evolution of each related technique. The main technical aspects, including feedstock properties, process control, post-treatments and energy source–material interactions, are also discussed. The technical challenges and advice about how to address these are presented. Comparisons are made between the techniques to facilitate the selection of the best ones in practical use. In addition, representative applications of the 3D printing of various types of ceramics are surveyed. Future directions are pointed out on the advancement on materials and forming mechanism for the fabrication of high-performance ceramic components.

3D printing of ceramics: A review

A deflectable beam spatial light modulator formed from a structure of a reflecting layer, typically metal, on a spacer layer, typically photoresist, which in turn is on a substrate containing electronic addressing circuitry is disclosed. Also, the method of fabrication including a plasma etch after dicing of the substrate into chips is disclosed.

Spatial light modulator

A light modulator comprising a light-reflective metallized membrane defining a deformable mirror disposed over a semiconductor substrate of one conductivity type in which a matrix array of field effect address transistors are formed, the metallized membrane cooperating with a matrix of floating metallic field plate members disposed on an insulating layer covering the substrate to define an array of air gap capacitors for line addressing by the field effect address transistors. The floating metallic field plates are opaque to light and prevent photocharge generation in the active regions of the matrix array of field effect address transistors. The metallized membrane is spaced from the field effect address transistors and the metallic floating field plates by an upstanding semiconductor grid structure which is formed on the insulating layer of the semiconductor substrate and defines gate electrodes for the address transistors. The metallized membrane is mounted on the upstanding semiconductor grid structure by molecular bonding to the contact members disposed over the semiconductor grid structure. The metallized membrane is formed of a polymer of nitrocellulose as a flexible carrier layer on at least one surface of which is disposed a thin metallic coating providing a light reflective surface. Each transistor in the array of field effect address transistors is line-addressable, and the metallized membrane in each cell of the matrix array of air gap capacitors is deflectable inwardly toward the substrate in response to the signal on the address transistor corresponding thereto. Should a potential above a predetermined magnitude be placed on an individual air gap capacitor, the metallized membrane will transfer charge to the floating field plate and return to zero deflection. The floating field plate thereby not only acts as a light-blocking layer, but also prevents voltage-induced collapse of the metallized membrane to the surface of the semiconductor substrate.

Deformable mirror light modulator

A spatial light modulator (10) of the DMD type having increased performance parameters. A pixel mirror (30) is supported by a yoke (32), whereby electrostatic attraction forces (70, 76, 80, 82) are generated between several structures. First, between the elevated mirror (30) and an elevated address electrode (50, 52). Second, between the yoke (32) and an underlying address electrode (26, 28). The pixel (30) achieves high address torque, high latching torques, high reset forces, and greater address margins over previous generation devices. The proximity of the yoke (32) over the substrate address electrodes (26, 28) realizes large attraction forces whereby the pixel is less susceptible to address upset, requires lower reset voltages and provides higher switching speeds.

Active yoke hidden hinge digital micromirror device

A brief overview of deformable-mirror spatial light modulator (SLM) technology is presented, followed by the first comprehensive review of the Texas Instruments deformable-mirror device (DMD), a subclass of deformable-mirror SLMs. The DMD architecture, fabrication, and operation (both analog and digital) are described. It is shown that amplitude-dominant or phase-dominant modulation is obtained by a simple modification of the pixel architecture. Representative DMD applications are presented.

Larry J. Hornbeck

Papers

Spatial light modulator and method

Spatial light modulator

Deformable mirror light modulator

Active yoke hidden hinge digital micromirror device

Deformable-Mirror Spatial Light Modulators