This article discusses the transition of a form of nanoimprint lithography technology, known as Jet and Flash Imprint Lithography (J-FIL), from research to a commercial fabrication infrastructure for leading-edge semiconductor integrated circuits (ICs) Leading-edge semiconductor lithography has some of the most aggressive technology requirements, and has been a key driver in the 50-year history of semiconductor scaling Introducing a new, disruptive capability into this arena is therefore a case study in a "high-risk-high-reward" opportunity This article first discusses relevant literature in nanopatterning including advanced lithography options that have been explored by the IC fabrication industry, novel research ideas being explored, and literature in nanoimprint lithography The article then focuses on the J-FIL process, and the interdisciplinary nature of risk, involving nanoscale precision systems, mechanics, materials, material delivery systems, contamination control, and process engineering Next, the article discusses the strategic decisions that were made in the early phases of the project including: (i) choosing a step and repeat process approach; (ii) identifying the first target IC market for J-FIL; (iii) defining the product scope and the appropriate collaborations to share the risk-reward landscape; and (iv) properly leveraging existing infrastructure, including minimizing disruption to the widely accepted practices in photolithography Finally, the paper discusses the commercial J-FIL stepper system and associated infrastructure, and the resulting advances in the key lithographic process metrics such as critical dimension control, overlay, throughput, process defects, and electrical yield over the past 5 years This article concludes with the current state of the art in J-FIL technology for IC fabrication, including description of the high volume manufacturing stepper tools created for advanced memory manufacturing

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Nanoimprint lithography steppers for volume fabrication of leading-edge semiconductor integrated circuits.

The importance of thermoelastic damping as a fundamental dissipation mechanism for small-scale mechanical resonators is evaluated in light of recent efforts to design high-Q micrometer- and nanometer-scale electromechanical systems. The equations of linear thermoelasticity are used to give a simple derivation for thermoelastic damping of small flexural vibrations in thin beams. It is shown that Zener’s well-known approximation by a Lorentzian with a single thermal relaxation time slightly deviates from the exact expression.

Thermoelastic Damping in Micro- and Nano-Mechanical Systems.

In this study, the results of protein adsorption on a wide spectrum of different surface-attached polymer networks are presented. The networks were generated from copolymers containing photoactive benzophenone groups or thermally activated azosulfonyl groups. The copolymers were deposited as thin films onto solid substrates and then (photo-)activated, which leads to crosslinking and the formation of surface-attached polymer networks. This simple preparation protocol allows the study of a wide range of polymer networks with well-defined hydrophilicity and/or charge and permits thus control of the degree of swelling in a contacting aqueous buffer solution. The so obtained polymer surfaces were exposed to solutions containing fibrinogen or other proteins and the amount of protein adsorbed was measured by surface plasmon resonance spectroscopy (SPR). It was found that strongly swollen polymer systems, which have only weak enthalpic interactions with the proteins, show strong protein repellency irrespective of the details of the chemical composition. We propose that conformational changes in the surface-attached polymer networks ('entropic shielding') and/or size exclusion effects dominate the adsorption behavior. In addition, we show first results of cell adhesion experiments of endothelial cells on these networks. It was found that surfaces which are protein resistant show also strong cell repellency, so that the surface-attached polymer networks might be used as a valuable tool to control cell adhesion.

Protein-resistant polymer surfaces

Memristors have recently begun to be explored in arithmetic applications. However, all prior designs for memristor-based gates have had shortcomings in terms of scalability, applicability, completeness, and performance. In this brief, a new low-power gate design, i.e., memristors-as-drivers gates, is proposed, which overcomes each of these issues by combining sense circuitry with the IMPLY operation. By sensing the values of the input memristors as the driver for the output memristor, the delay is reduced to a single step for any Boolean operation, including xor. The area is reduced to at most three memristors for each gate and consumes only 30 fJ. An ${N}$-bit ripple carry adder implementation is proposed, which uses these gates to achieve a total delay of ${N}+1$ with an area of 8${N}$ memristors and their drivers. The individual bits of the proposed adder can be also pipelined, reducing the latency to four steps per addition.

MAD Gates—Memristor Logic Design Using Driver Circuitry

Journal of Micromechanics and Microengineering: Editorial

This paper presents the characterization, optimization, and fabrication of phase change material (PCM) germanium telluride (GeTe) based RF switches investigating the materials’ aspect and design parameters of the switches and their impact on the RF performance. Surface properties of GeTe thin films are investigated through atomic force microscopy (AFM), scanning electron microscopy (SEM), and cross-wafer resistance mapping measurements. Optimized GeTe thin films exhibit over five orders of resistance change. Various GeTe switch design constraints are studied via cross sectioning of the fabricated device using a focused ion beam (FIB)-SEM. Current-carrying capacity and resistance of microheaters are extracted using electrical characterization. The RF performance of the PCM switches is optimized using diverse design parameters and characterization of PCM thin films. A six-layer microfabrication process is presented for monolithically integrating RF circuits with PCM switches. Methods to reduce parasitic elements in PCM switches are discussed. The RF performance of the optimized PCM based switch is simulated and measured demonstrating better than 0.4 dB of insertion loss and a return loss better than 20 dB from dc to 67 GHz.

Characterization, Optimization, and Fabrication of Phase Change Material Germanium Telluride Based Miniaturized DC–67 GHz RF Switches

This article reports the first implementation of 3-bit millimeter-wave switched true-time-delay (TTD) phase shifters based on phase-change material (PCM) germanium telluride (GeTe). Two TTD phase shifters are presented. The first phase shifter is designed using four monolithically integrated PCM single-pole triple-throw (SP3T) switches to route the signal through delay lines. The insertion loss variation between various states is minimized by integrating two fixed PCM GeTe elements maintained in the crystalline state, along with the optimized width of the delay lines. The PCM switching cells are latching type, thus, consume no static dc power. The SP3T switches are connected back-to-back in two stages to provide a 3-bit phase shift with 20° precision. The second phase shifter is designed using two back-to-back connected PCM single-pole eight-throw (SP8T) switches. Both phase shifters are designed to operate over an 8 GHz wide frequency band with a center frequency of 30 GHz. The devices are fabricated in-house using an eight-layer microfabrication process. The proposed devices are highly miniaturized with an overall device area of 0.42mm
 2
 and 1.4mm
 2
 for the first and second phase shifter, respectively. The first phase shifter exhibit a measured average loss of 4.3 dB with a variation of ±0.3 dB and a return loss better than 20 dB, while the second phase shifter demonstrates low average measured loss of 3.8 dB with only ±0.2 dB loss variation and returns loss better than 17 dB at 30 GHz. Both phase shifters provide 180° linear phase shift with lower than 18 ps delay in the worst case.

Loss Compensated PCM GeTe-Based Latching Wideband 3-bit Switched True-Time-Delay Phase Shifters for mmWave Phased Arrays

This article presents an approach to monolithically implement radio-frequency (RF) phase change material (PCM) germanium telluride (GeTe) T-type switch as a switching unit cell for millimeter-wave (mmWave) redundancy switch matrix applications. The miniature T-type switch demonstrates three states of operation, including one crossover state and two turn states. A seven-layer microfabrication process, including an additional conductive layer to reduce the $RC$ time constant due to the bias network routing, is developed and optimized to fabricate the multiport RF devices. A $4 \times 6$ PCM-based redundancy switch matrix is developed by monolithically integrating four T-type switches in the cascade configuration. Thermal crosstalk in PCM switches is experimentally investigated using submicrometer spatial resolution transient thermal imaging. The presented T-type switch has the device periphery of 0.55 mm $\times \,\,0.55$ mm, while the overall integrated PCM redundancy switch matrix is fabricated with a device footprint of 0.88 mm $\times \,\,1.1$ mm. The measured results of the T-type switches demonstrate an excellent RF performance with lower than 1.6 dB insertion loss, better than 20 dB return loss, and higher than 20 dB isolation in all states from dc–67 GHz. The redundancy switch matrix exhibits an insertion loss less than 3 dB, return loss better than 14 dB, and isolation higher than 20 dB from dc–60 GHz. To the best of our knowledge, this is the first implementation of a PCM-based redundancy switch matrix.

Miniaturized DC–60 GHz RF PCM GeTe-Based Monolithically Integrated Redundancy Switch Matrix Using T-Type Switching Unit Cells

This article presents a monolithically integrated reflective-type phase shifter (RTPS) utilizing silicon-on-insulator (SOI) radio frequency (RF) microelectromechanical systems (MEMS). The analog phase shifter employs a hybrid coupler and two identical reflective loads optimized to achieve a large phase shift range. The hybrid coupler is designed using two CPW-based couplers connected in a folded tandem configuration to achieve a compact size design. Various reflective load topologies are studied for optimum phase shift range and phase linearity over the bandwidth of interest. Measurement results demonstrate a continuous 120° tunable range from 26 to 30 GHz. The mmWave phase shifter exhibits a low insertion loss of 5.35 dB ± 0.6 dB at 28 GHz. The fabricated phase shifter has an overall device footprint of 4.0 $\text {mm}\times 2.6$ mm. All the components of the phase shifter module are co-fabricated in the 20 $\mu \text{m}$ device layer of a SOI wafer, which provides the flexibility of monolithic integration with other RF modules in phased array antenna systems. Contactless thermally actuated MEMS varactors are used in the reflective loads which do not suffer from the conventional contact-based reliability issues.

Thermally Actuated SOI RF MEMS-Based Fully Integrated Passive Reflective-Type Analog Phase Shifter for mmWave Applications

Compact inline chalcogenide radio-frequency (RF) phase-change material (PCM) switches utilizing germanium telluride (GeTe) in series and shunt configurations are reported in this paper. Phase transition in PCM has been achieved by electrically isolated embedded micro-heaters. RF-PCM switches presented exhibit ON-state resistance of 2.4 ohm and OFF-state capacitance of 8.5 fF. The estimated cut-off frequency $(F_{\mathrm{co}})$ is 7.8 THz, which is 10 times higher than state-of-the-art RF CMOS switches. The RF-PCM series and shunt switches are simulated and measured, demonstrating ON-state insertion loss less than 0.3 dB and 0.2 dB and OFF-state isolation higher than 20 dB and 36 dB over DC–26 GHz frequency range respectively.

Tejinder Singh

Papers

Characterization, Optimization, and Fabrication of Phase Change Material Germanium Telluride Based Miniaturized DC–67 GHz RF Switches

Loss Compensated PCM GeTe-Based Latching Wideband 3-bit Switched True-Time-Delay Phase Shifters for mmWave Phased Arrays

Miniaturized DC–60 GHz RF PCM GeTe-Based Monolithically Integrated Redundancy Switch Matrix Using T-Type Switching Unit Cells

Thermally Actuated SOI RF MEMS-Based Fully Integrated Passive Reflective-Type Analog Phase Shifter for mmWave Applications

Chalcogenide Phase Change Material GeTe Based Inline RF SPST Series and Shunt Switches