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Fig. 4: Dynamic pattern from the array projected on a Fig. 3: (top left) The assembled DPG device, the central scintillation screen (Left). A line pattern printed in resist (Right) rectangular slit is the 256x4096 lenslet array. (bottom left) fab in Leuven (Belgium) on top of 65nm technology CMOS a cut through the device shows the CMOS layers with wafers from TSMC. Devices were delivered ready for mounting onto the e-beam tool. After electrical performance tests, the first the microlenses on top. (right) view inside a few of the devices were mounted into the column and operated success- microlenses. fully and first printing results were shown. The delivery of the challenges related to the fragility of the underlying cMOs cir- first fully functional micro-lens arrays on top of the DPG logic cuit, the need for very low resistive connections to operate the chip is a major leap for the rEBl tool development. it enabled device, and packaging requirements. imec was able to manu- the dynamic printing of arbitrary patterns in resist on a mov- facture the micro-lens array on top of functional cMOs wafers ing wafer stage. Figure 4 shows some of the initial patterning as shown on figure 3. Processing was done in imec’s 300mm results obtained in the course of this project. Here comes the next generation MEMS Oscillators: pMEMS By harmeet Bhugra OVEr thE past sEVEral decades, quartz crystal resonators (XTALs) and oscillators (XOs) have been used for frequency ref- erence applications in almost all electronic systems due to their stability and superior electrical performance such as low phase noise and frequency stability. to overcome performance limita- tions and to resolve quartz oscillator reliability issues, several alternative technologies have been trying to replace quartz in recent years, including MEMs oscillators and cMOs oscillators. Fig. 1: Schematic view of a pMEMS resonator. these new disruptive technologies provide better robust- ness against shock and vibration, smaller form-factor, and the potential of monolithic integration. compared to the quartz pMEMS resonator counterparts, however, their performance needs to be improved as the name implies, the pMEMs resonator is composed of especially for high frequency reference applications. piezo- a piezoelectric material (AlN) with single crystal silicon (SCS), electrically transduced pMEMs resonators have emerged as taking advantage of both worlds, i.e., combines the advan- one of the strong candidates for replacing quartz technology tages of piezoelectric quartz resonators and the advantages of for high–frequency, low phase noise reference applications. in silicon MEMs resonators. Unlike typical pure silicon capacitive this paper, we introduce the design principles and performance resonators, pMEMS resonators do not require any DC bias volt- characteristics of pMEMS oscillators developed at IDT. Shock age for operation. These composite pMEMS resonators offer and vibration tests, as well as long-term stability measurements, better motional impedance and linear power handling, and have have proven pMEMS oscillators to be reliable and cost-effective demonstrated excellent long-term frequency stability. Benefiting replacements for quartz crystal oscillators in high-frequency from the strong electromechanical coupling of the piezoelectric timing reference applications. material and stability and low damping of scs, pMEMs resona- tors offer very low motional resistance and an excellent quality Harmeet Bhugra is a Managing Director at IDT and is factor. Figure 1 presents the schematic illustration of a pMEMs responsible for the vision, growth and general management of resonator with the piezoelectric layer and electrodes stacked on the MEMs business - www.idt.com top of the scs layer. www.electronics-eetimes.com Electronic Engineering Times Europe December 2012 35


EETE DECEMBER 2012
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