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3D XPoint uses PCM Material in ReRAM Device

January 31st, 2016

IM Flash pre-announced “3D XPoint”(TM) memory for release later this year, and lack of details has led to widespread confusion regarding what it is. EETimes has reported that, “Chalcogenide material and an Ovonyx switch are magic parts of this technology with the original work starting back in the 1960’s,” said Guy Blalock, co-CEO of IM Flash at the 2016 Industry Strategy Symposium hosted by the SEMI trade group. However, contradicting industry terminology conventions, in another article EETimes reported that a spokesperson for Intel has said that, “3D XPoint should not be described as ReRAM.”
First promoted by the master of materials solutions-looking-for-problems Sanford Ovshinsky under the name “Ovonic” trademark, chalcogenide materials form glassy structures with meta-stable properties. With proper application of heat and electrical current, chalcogenides can be made to switch between low-resistivity crystalline and high-resistivity amorphous phases to create Phase-Change Memory (PCM) arrays in silicon circuit architectures. Chalcogenides can also function as the matrix for the diffusion of silver ions in a cross-point device architecture to create a digital “Resistive RAM” (or “ReRAM” or “RRAM”), or create an analog memristor for neuromorphic applications as explored by Prof. Kris Campbell of Boise State in collaboration with Knowm.

Hitachi and Renesas Technology developed Phase-Change Memory (PCM) cell technology employing Ta2O5 interfacial layer to enable low-power operation. (Source: Hitachi) Hitachi and Renesas Technology developed Phase-Change Memory (PCM) cell technology employing Ta2O5 interfacial layer to enable low-power operation. (Source: Hitachi)

The Figure shows a schematic cross-section of a typical PCM cell. From a scientific perspective, we could say that any memory cell that relies upon a change in material phase to encode digital data should be termed a PCM. However, due to the history of this specific type of PCM device being the only architecture explored for decades (and commercialized for limited niche sub-markets), and due to the fundamentally different circuit architectures, it is reasonable to categorically deny that any cross-point device is a “PCM.”
However, any cross-point memory device based on a resistance change has to be a ReRAM regardless of the switching phenomenon:  phase-change, filament-growth, ion-diffusion, etc. So we could say that this new chip uses PCM material in a ReRAM device.
—E.K.

Controlling Polymers to Tune TFTs

January 16th, 2016

Thin-film transistors (TFT) created using only additive process steps could create new low-cost ICs with functionalities beyond silicon, but only if we understand how to control structures at the molecular level. Thin films of conjugated polymers such as poly(3-hexylthiophene) (P3HT) can provide useful conductivity when the electron mobilities are controlled within as well as between molecules. In producing TFTs using such organic macromolecules, we must rigorously control the deposition and annealing processes so that the right molecules line up in the right order.
Peter F. Green, Professor of Chemical Engineering, Macromolecular Science and Engineering at the University of Michigan, and his team fabricated ~55 nm thin films of P3HT using resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE), as well as conventional spin-casting. The films produced by MAPLE show a higher degree of structural disorder, with localized trap sites that reduce mobility out-of-plane by an order of magnitude compared to spin-cast films.

(Source: Peter Green, University of Michigan) (Source: Peter Green, University of Michigan)

The Figure shows that despite the disorder of MAPLE-deposited P3HT, enhanced carrier density at the dielectric interface allows TFTs to exhibit similar in-plane mobilities to those built using conventionally spin-coated films. TFTs were top-contact, bottom-gate designs on 300nm thermal oxide on highly doped silicon. In-plane carrier mobilities of MAPLE-deposited versus spin-cast films were 8.3 versus 5.5 (×10 -3 cm2/V/s). In principle, the ability to independently control in- and out-of-plane mobilities allows for the fine tuning of TFT parameters for different applications.
—E.K.

CMOS-Photonic Integration Thermally Sensitive

December 31st, 2015

As published in the journal Nature, CMOS transistors have been integrated with optical-resonator circuits using complex on-chip sensors and heaters to maintain temperature to within 1°C. While lacking the laser-source, these otherwise-fully-integrated solutions demonstrate both the capability as well as the limitation of trying to integrate electronics and photonics on a single-chip. The Figure shows a simplified schematic cross-section of the device.

Full chip cross-section (not to scale) from the silicon substrate to the C4 solder balls, showing the structures of electrical transistors, waveguides, and contacted optical devices. The minimum separation between transistors and waveguides is <1 μm, set only by the distance at which evanescent light from the waveguide begins to interact with the structures of the transistor. Full chip cross-section (not to scale) from the silicon substrate to the C4 solder balls, showing the structures of electrical transistors, waveguides, and contacted optical devices. (Source: Nature)

Lead author Chen Sun—affiliated with UC Berkeley and MIT, as well as with commercial enterprise Ayar Labs, Inc.—developed the thermal tuning circuitry, designed the memory bank, implemented the ‘glue-logic’ between various electronic components, and performed top-level assembly of electronics and photonics. The main limitation is the temperature control, since deviation by more than 1°C results in loss of coupling that otherwise provides for P2M/M2P transceivers:

* Waveguide Loss – 4.3 dB/cm,
* Tx and Rx Data Rate – 2.5 Gb/s,
* Tx Power – 0.02 pJ/bit,
* Rx Power – 0.50 pJ/bit, and
* Ring Tuning Control Power – 0.19 pJ/bit, so
* Total power consumption = 0.71 pJ/bit.

The Register reports that this prototype has a bandwidth density of 300 Gb/s per square millimetre, and needs 1.3W to shift a Tb/s straight from the die to off-chip memory. A single chip integrates >70 million transistors and 850 photonic components to provide microprocessor logic, memory, and interconnect functions.

—E.K.

Apple Fab Speculation

December 18th, 2015

Apple Corp. recent purchased an old 200mm-diameter silicon wafer fab in San Jose capable of creating as small as 90nm device features. Formerly owned and operated by Maxim, the US$18.2M purchase reportedly includes nearly 200 working fab tools. Some people outside the industry have speculated that Apple might use this fab to do R&D on the A10 or other advanced logic chips, but this old tool-set is completely incapable of working on <45nm device features so it’s useless for logic R&D.

As reported at EETimes, this old fab could be used for the R&D of “mixed-signal devices, MEMS and image sensors and for work on packaging.” Those who know do not speak, while those who speak do not know…I do not know so I’m free to join the public speculation. Mixed-signal and MEMS processing would require major re-tooling of the line, but this 15-20 year-old tool-set is nearly turn-key for wafer-level packaging (WLP). With minimal re-tooling, this line could produce through-silicon vias (TSV) or through-mold vias (TMV) as part of Fan-Out WLP (FO-WLP).

Our friends at ChipWorks have published a detailed tear-down analysis of the System-in-Package (SiP) used in the first generation Apple Watch; it contains 30 ICs and many discretes connected by a 4-layer printed circuit board (PCB). Significant power and performance improvements in mobile devices derive from stacking chips in such dense packages, and even greater improvements can found in replacing the PCB with a silicon interposer. With Apple pushing the limits on integrating new functionalities into all manner of mobile devices, it would be strategic to invest in WLP R&D in support of application-specific SiP design.

—E.K.

MPU Cores and Legal Boors

November 30th, 2015

As reported by The Register, AMD has been sued by a customer who claims that the number of Bulldozer cores in some Opteron and FX microprocessor (MPU) chips are fewer than advertised. The claim is based on the argument that a “real” MPU core has it’s own floating point unit for calculations, and that consumers were misled by product claims. I am not a lawyer (IANAL) and have no connections to either side in this case, but AMD’s website (http://www.amd.com/en-us/products/processors/desktop/fx#) now clearly indicates that cores share a Floating Point (FP) scheduler.

The Figure shows that the confusion is due to the design of the Bulldozer microarchitecture wherein a pair of cores is called a module, and each pair shares a branch prediction engine, an instruction fetch and decode stage, a floating-point math unit, a cache controller, a 64K L1 instruction cache, a microcode ROM, and a 2MB L2 cache. The lawsuit claims, “Because AMD did not convey accurate specifications, tens of thousands of consumers have been misled into buying Bulldozer CPUs that do not conform to what AMD advertised, and cannot perform the way a true eight core CPU would (i.e., perform eight calculations simultaneously).”

AMD_Bulldozer_floorplan
This is analogous to someone buying a car with a V8 internal combustion engine, and then suing the manufacturer because there are only 4 fuel injectors and not all cylinders fire simultaneously. The claim that “true” multi-cores must be capable of functioning simultaneously is like claiming that “true” multi-cylinder engines must be capable of all cylinders firing simultaneously. AMD has officially responded with the statement that, “We believe our marketing accurately reflects the capabilities of the Bulldozer architecture which, when implemented in an 8-core AMD FX processor, is capable of running eight instructions concurrently.” There seems to be little legal difference between “simultaneously” and “concurrently” but IANAL.

Sure, there’s a technical difference and likely a slight performance benefit to direct fuel injection into each cylinder, but raw performance is only one aspect of the design trade-offs between performance and cost and reliability. Sharing 1 fuel injector between 2 cylinders often provides an optimum of performance/cost/reliability in internal combustion engines. Sharing 1 FPU between 2 logic cores seemingly provides an optimum of performance/cost/reliability in CPUs.

—E.K.

Thermoplastically Deformable Electronic Circuits

November 27th, 2015

Philips is testing a technology developed by imec and CMST (imec’s associated lab at Ghent University) to create low-cost 3D LED packages. As shown at last month’s International Microelectronics Assembly and Packaging Society (IMAPS 2015) meeting, these thermoplastically deformable electronic circuits are already being integrated by Philips into LED lamp carriers, a downlight luminaire, and a omnidirectional light source.

Miniature dome test vehicle with integrated low power LEDs, (a) circuit before forming, and (b) circuit after vacuum forming using a 40mm half-sphere mold. (Source: imec) Miniature dome test vehicle with integrated low power LEDs, (a) circuit before forming, and (b) circuit after vacuum forming using a 40mm half-sphere mold. (Source: imec)

The technology is based on meander-shaped interconnects, which are patterned using  standard printed circuit board (PCB) production equipment and then sandwiched between 2D thermoplastic polymer (e.g. polycarbonate) sheets. The Figure shows one example in final form after vacuum thermoforming into a 40mm half-sphere mold.
This is a glorious example of “elegant engineering” where a clever combination of materials and processes has been integrated with highly desirable characteristics:  low tooling cost, low direct material cost, easily scalable from lab to fab, low product weight, and high product resilience. This seems to represent almost a new industrial product category that combines a “package” and a PCB.

 

—E.K.

Nowhere Near Room Temp Superconductors

October 30th, 2015

On-chip metal interconnects limit IC speed in many advanced design today, and with signal delay proportional to the product of the resistance (R) of wires and the capacitance (C) of dielectric insulation, wires with R lower than that of copper (Cu) metal would significantly improve IC performance. We know of superconductors—materials with zero resistance to electrical current flow—but only at “critical temperature” (Tc) well below 77°K, and so there has been an ongoing quest by scientists to find a material with Tc above room temperature of 298°K.

Sadly, after 4 years and nearly 1000 materials tested, a team of 6 Japanese research groups led by Hideo Hosono from the Tokyo Institute of Technology found no room temperature superconductors. They did find 100 previously unknown superconductors with Tc <56°K, and they published crystal structures and phase diagrams of all materials studied to help other researchers avoid now known dead-ends (DOI: 10.1088/1468-6996/16/3/033503).

Other researchers continue to explore the possibilities of using one-dimensional (1D) carbon-based materials such as carbon-nano-tubes (CNT) or graphene as on-chip conductors. So far, there are extreme difficulties in controlling the growth of such 1D structures within interconnect patterns, and additional challenges with forming ohmic contacts between CNT and Cu lines across billions of connections in a modern IC. More science is seemingly needed to find new paths before the engineers can explore those paths to find better solutions. Meanwhile…for the next few years at least…expect Cu metal to be the continued choice for nearly all multi-level metal interconnects on chip.

—E.K.

EUV Cost at 1000 Daily Exposures

October 26th, 2015

On October 14, 2015, ASML Holding N.V. (ASML) published its 2015 third-quarter results:  Q3 net sales of €1.55 billion with gross margin of 45.4% (in line with guidance), and guided Q4 2015 net sales at approximately €1.4 billion and a gross margin of around 45%. Due to mismatched financial analyst expectations, Bloomberg reported that ASML’s stock price dropped ~7% in a single day of trading, despite the company also reporting upgrades to both the TWINSCAN NXT 193nm-immersion (193i) and the NXE Extreme Ultraviolet (EUV) tools. In particular, a new record of 1000 wafer exposures in a single day was set by one EUV tool.

The science of controlling the 13.54nm wavelength electromagnetic radiation that we like to call “Extreme Ultra-Violet” or “EUV” (instead of the colloquial scientific term “soft x-ray”) is inherently challenging. The engineering of EUV Lithography is not just challenging but bordering on inherently impossible:  from exploding tin plasma source, to all-reflective lenses that absorb energy, to the trade-offs in mask pattern protection. The team at ASML working on the exposure tool—along with the different specialist organizations still working on improved sources, masks, and resists—deserve the industry’s unwavering admiration for the important work they do every day.

In a prepared statement, ASML President and Chief Executive Officer Peter Wennink said, “We have proven the capability both to expose 1,000 wafers per day and, in a manufacturing readiness test, to expose 15,000 wafers in four weeks. We have also achieved a four-week average availability of more than 70 percent  at multiple customer sites. The first shipment of our fourth-generation EUV lithography system, the NXE 3350B, is in progress, with two more expected to ship in Q4.”

Still, progress along desired EUV roadmaps continues to be slow, and the competitive target shifts when the 193i exposure tool gains a 10% throughput improvement to 275 wafer-passes/hour (wph). When the 193i tool gains a 30% overlay improvement, that means double-patterning based on litho-etch-litho-etch (LELE) process flows gain in pattern fidelity. Since ASML provides both technologies, delays in orders for EUV just means more sales of 193i tools.

Let’s play with the numbers here…275 wph x 20 hours x 30 days = 165k wafer-passes/month for the NXT:1980. The NXE:3350B can current handle 15k wafer-passes/month. So even if the tools were equally priced, just based on tool depreciation each EUV exposure today costs >10x that of a 193i exposure, which is why pitch-splitting multi-patterning 193i continues to dominate.

—E.K.

Leti Shows MEMS on 300mm Wafers

September 30th, 2015

As reported by EETimes from the European MEMS Summit last month, French research institute CEA-Leti has manufactured accelerometer MEMS devices on 300mm-diameter wafers. This technology is currently being transferred to Tronics Microsystems SA (Grenoble, France), which currently only manufactures on 200mm wafers. Since CEA-Leti has long functioned as the R&D group for STMicroelectronics (ST), and previously led the way for ST to produce MEMS chips on 200mm-diameter wafers, we may expect that 300mm-wafer MEMS processing is now on ST’s internal roadmap.
Moving production to larger wafers makes sense when either the chip-size or the manufacturing volume increase in size. Much of the growth in demand for MEMS is for so-called “combo” sensors that combine multiple sensor technologies, such as CEA-Leti’s piezo-resistive silicon nanowire technology which allows the accelerometer, gyroscope, magnetometer, and pressure sensor capability to be integrated on the same chip.
The compatibility of Leti’s 200mm-developed technologies with 300mm wafer fabrication, “shows a significant opportunity to cut MEMS production costs,” said Leti CEO Marie Semeria in a press release. “This will be especially important with the worldwide expansion of the Internet of Things and continued growing demand for MEMS in mobile devices.” Sensors of all sorts will be needed for all of the different “Things” to be able to capture new useful information, so we may expect that demand for combo MEMS devices will continue to increase.
—E.K.

Silex’ Strategic Acquisition by China

September 25th, 2015

A secretive investment holding company out of Hong Kong named GAE Ltd has acquired 98% of the shares in Silex Microsystems AB (Jarfalla, Sweden). The transaction took place on July 13th of this year when the former major shareholders agreed to sell all of their respective holdings, while Silex founder and CEO Edvard Kalvesten retains 2% of the shares in the company and continues his role as CEO and board member of Silex. No changes are made to the organizational structure or business operations of Silex, while the new owners plan to build a new high-volume manufacturing line near Beijing that clones the equipment and processes in Sweden with first wafers out by mid-2017 (as reported at EETimes).

Silex claims to be the “world’s number one Pure Play MEMS Foundry”, has worked with AMFitzgerald&Assoc. on RocketMEMS shuttle wafers to reduce MEMS development time by 6-12 months, and has developed multiple Through-Silicon Via (TSV) technologies to allow for efficient 3D integration of MEMS and CMOS.

Almost lost as a footnote in the news is that Silex holds IP on lead-zirconium-titanate (PZT) thin-film technology that allows for efficient piezo-electric energy-harvesting chips. MicroGen Systems is currently in the market with aluminum-nitride (AlN) piezo-cantilever micro-power generator system to power IoT nodes by scavenging either single-frequency or multi-frequency vibrations, working with X-Fab in Germany as foundry partner. If PZT-based piezo-cantilever energy harvesters can compete with AlN-based devices then the former could constitute much of the product volume in the new Silex Beijing fab. In 2014, Yole Developpement forecast “the integration of IoT-dedicated electronic components to result in a market volume of 2B units for these devices by 2021;” if 30% will use energy harvesting then this represents 600M units globally.

—E.K.

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