![3D NAND flash memory array, based on TCAT [1], with 16 cells per string, top gate-select layer and bottom source-select layer.](https://www.coventor.com/wp-content/uploads/2014/05/TCAT_whole_bf-M1-marked1-80x80.png)
Challenges in 3D NAND Flash Processing
May 23, 2014
Linking Virtual Wafer Fabrication Modeling with Device-level TCAD Simulation
July 3, 2014
Coventor attended the Solid State Sensors, Actuators and Microsystems Conference last week, known simply as “Hilton Head” to the North American MEMS and nanotechnology community. This is a delightful conference held every two years at the same beachfront resort on Hilton Head Island, South Carolina. The location and single track of oral presentations create a congenial atmosphere for engaging with other participants.
At the opening, the conference chair Professor Mehran Mehregany of Case Western Reserve noted that this was the 30th anniversary of the conference and remarked on the incredible technical progress over that period. In 1984, the year of the first conference, MEMS products were only a gleam in the eyes of a select group of researchers. Today, MEMS ship in the billions and are ubiquitous in automobiles, mobile devices, and many other products. Professor Mehregany then asked the assembled micro- and nanotechnology research community a provocative question: Now that MEMS have become a reality, what should we do for the next 30 years? To help the research community answer this question, the organizers assembled a panel of four science fiction writers who shared their speculations on what might be possible in 30 years.
I won’t add my own speculations to the 30-year forecast, but rather focus on a couple trends that were evident in the conference that are likely closer to commercial reality, say within 10 years or less. One trend revolves around various approaches to achieving high-Q in piezo-mechanical oscillators for timing reference applications. The second trend consists of efforts by multiple research groups to microfabricate ultra-precise, navigation-grade gyroscopes. Both of these trends were spurred by a DARPA initiative that started a few years ago to develop precision gyroscopes and timing solutions, both of which are required to enable micro-scale, high-precision, inertial-navigation systems. The fruits of this program were on display at the conference.
MEMS Resonators for Timing
The timing reference market is dominated today by quartz crystal devices, but MEMS-based timing solutions from companies like SiTime, Discera and IDT are expected to grab 5-10% of the $6 billion market in 2015. A critical performance metric for timing references is the temperature coefficient of frequency (TCF). Essentially, TCF is the change in the reference frequency with change in temperature, and it is measured in parts per million (ppm) per degree C for consumer-grade timing references. Roughly speaking, the goal of the DARPA-sponsored effort is to achieve much lower TCF, measured in parts per billion (ppb) per degree C. We listened with considerable interest to reports from multiple research groups on their efforts to develop piezo-MEMS resonators that achieve high quality factor, Q, and ultra-low TCF. Most of these groups are currently researching piezo-MEMS resonators based on aluminum nitride (AlN) as the piezo material, but some are using more exotic materials like gallium nitride (GaN). In subsequent conversations, we learned that all of these groups are struggling to simulate the frequency response of their piezo-mechanical designs using general-purpose finite element tools. As it turns out, CoventorWare includes a very efficient technique for simulating the frequency response of piezo-mechanical resonators and therefore directly addresses the challenge these groups face. We look forward to engaging with these groups to try out the CoventorWare solution.
High-Precision Gyroscopes
Gyroscopes are classified into four groups according to their bias drift precision: consumer, tactical, navigation and strategic. The low-cost MEMS gyros shipping today are consumer grade, the least precise category, but a group headed by Andre Shkel at U.C. Irvine has developed a quad-mass MEMS gryo that is capable of achieving tactical grade precision. Several other research efforts focused on techniques for microfabricating hemispherical gyros patterned after the larger conventionally machined hemispherical gyros that are dominant in navigation-grade applications. The conventionally machined hemispherical gyros are in the range of 3-5 cm diameter in comparison to 0.7 to 1cm diameter for the micro-fabricated hemispherical devices reported at this conference. That’s a significant size reduction, and likely manufacturing cost reduction as well. With continued development, these devices could take over industrial, aerospace and defense applications. Their size, and especially thickness, not to mention cost, probably precludes application in consumer mobile devices any time soon. But who knows what another 30 years of technical progress will bring?
![Fig. 2. Silicon spin qubit centered in the dotted circle, control and readout signals (M, P, R, T, and Q) are shown in the inset. Simplified schematics of the quantum point contact and corollary circuits are shown. The voltage source is implemented as a digital-to-analog converter at room temperature. (Taken from [6])](https://www.coventor.com/wp-content/uploads/2022/05/Fig.-2.-Silicon-spin-qubit-centered-in-the-dotted-circle-control-and-readout.png)
![Figure 2: Schematic view of standard CMOS including an electro-mechanical switch monolithically integrated into BEOL [2]. Courtesy: University of California, Berkeley](https://www.coventor.com/wp-content/uploads/2022/04/Figure-2-April-2022-MEMS-Blog-for-Coventor-website.png)
