Eun Chul Park

Fully integrated low phase-noise VCOs with on-chip MEMS inductors

We present fully integrated high-performance voltage-controlled oscillators (VCOs) with on-chip microelectromechanical system (MEMS) inductors for the first time. MEMS inductors have been realized from the unique CMOS-compatible MEMS process that we have developed to provide suspended thick metal structures for high-quality (Q) factors. Fully integrated CMOS VCOs have been fabricated by monolithically integrating these MEMS inductors on the top of the CMOS active circuits realized by the TSMC 0.18-/spl mu/m mixed-mode CMOS process. Low phase noise has been achieved as -124 and -117 dBc/Hz at 300-kHz offset from carrier frequencies of 1 and 2.6 GHz, respectively, in the fabricated single-chip VCOs.

Hermetically sealed inductor-capacitor (LC) resonator for remote pressure monitoring

This paper reports an integrated inductor-capacitor (LC) resonator structure fabricated using bulk micromachining and anodic bonding technologies. In this resonator structure, pressure change monitored by a capacitive pressure sensor results in the change of resonance frequency. The resonance frequency shift is detected by inductive coupling from an external transmission coil; therefore, pressure can be monitored remotely using the passive LC resonator. The fabricated device size measures 3 mm×3 mm×0.6 mm, and pressure responsivity has been estimated to be 2 MHz/mmHg. This micromachined, hermetically sealed structure is suitable for biomedical applications such as intraocular, cardiovascular and brain pressure monitoring.

Performance comparison of 5GHz VCOs integrated by CMOS compatible high Q MEMS inductors

In this paper, we report the performance comparison of 5 GHz CMOS VCOs fabricated by 0.18 /spl mu/m six-metal mixed-mode RF CMOS processes with respect to the same VCOs integrated with high Q MEMS inductors. The CMOS inductors implemented by a top-level 2 /spl mu/m-thick Al/Cu metal layer typically show Q factors of about 10, while the MEMS inductors can give much higher Q factors over 25. Differential CMOS VCO circuits have been optimally designed for the respective Q factors of both CMOS and MEMS inductors. Phase noise has been measured and compared for the fabricated VCOs, demonstrating that the VCOs with MEMS inductors can give better phase noise by more than 7 dB in the offset frequency range from 30 kHz to 3 MHz.

A low loss MEMS transmission line with shielded ground

This paper reports a MEMS transmission line with shielded ground realized using fully CMOS compatible, monolithically integrable 3-D RF MEMS processes. The fabricated transmission line has achieved extremely low loss by shielding the signal line from lossy silicon substrate at the bottom as well as from radiation into open air space above. A low loss of 0.35 dB/cm at 25 GHz has been achieved in the fabricated transmission lines.

Cross-coupled differential oscillator MMICs with low phase-noise performance

LC-tank oscillators in the 5/spl sim/6 GHz frequency range have been designed and implemented in a commercial 0.6 /spl mu/m GaAs MESFET technology. One is a voltage-controlled oscillator (VCO), and the other is an oscillator without a controlling element. The output frequency range of the VCO is from 5.44 to 6.14 GHz, and the measured phase-noise is -101.67 dBc/Hz at an offset frequency of 600 KHz from the 5.44 GHz carrier. The phase-noise of the 6.44 GHz oscillator is -108 dBc/Hz at an offset frequency of 600 KHz, and the phase-noise curve, in the offset frequency range between 100 KHz and 1 MHz, shows a -20 dB/decade slope. These phase-noise characteristics are comparable to, or better than, those of the reported 5/spl sim/6 GHz-band CMOS oscillators. To our knowledge, this is the first GaAs MESFET-based oscillator which has a cross-coupled differential topology and a capacitive coupling feedback to suppress the up-conversion of 1/f noise. Also, it is first reported that the GaAs MESFET-based oscillator shows 1/f/sup 2/ phase-noise behavior across the offset frequency range from 100 KHz to 1 MHz.

AFM probe tips using heavily boron-doped silicon cantilevers realized in a bulk silicon wafer

In this paper, we report a new method of fabricating AFM (Atomic Force Microscope) probe tips at low cost. Most of previous AFM probe tips have been made of SOI wafers using back-side anisotropic silicon etch. Therefore, the wafer cost is high and the dimension control is poor because the tip length and thickness depend on wafer thickness variation and etch non-uniformity during the tip formation, respectively. In this paper we propose a new fabrication process in which probe tips are formed selfaligned to the p/sup +/ (heavily boron-doped) cantilevers from the front-side etch of a bulk silicon wafer.

Low phase noise CMOS distributed oscillators using MEMS low loss transmission lines

For the first time, low noise distributed oscillators for millimeter wave signal generation have been realized by using fully IC compatible, monolithically-integrable 3-D RF MEMS transmission lines. The active core circuits of the distributed oscillators have been fabricated using 0.18 /spl mu/m CMOS processes. On the top of this CMOS circuits, low-loss MEMS transmission lines have been monolithically integrated suspending by 25 /spl mu/m. Phase noise of the fabricated MEMS distributed oscillators has been measured as -125.7 dBc/Hz at 1 MHz offset frequency from oscillation frequency of 13 GHz. This is the lowest phase noise ever reported on distributed oscillators implemented in CMOS technology.

Atomic Force Microscope Probe Tips Using Heavily Boron-Doped Silicon Cantilevers Realized in a Bulk Silicon Wafer

A new method of fabricating atomic force microscope (AFM) probe tip is presented. In this process, the probe tips were implemented using self-aligned heavily boron-doped silicon cantilevers in a bulk silicon wafer. In this structure, a stress-free cantilever can be easily defined by selective etch stop by the heavily boron-doped region in an anisotropic silicon etchant. The proposed tips do not require expensive silicon on insulator (SOI) wafers and double-side alignment. The probe tip dimensions can be exactly defined regardless of wafer thickness by the self-aligned etch from the front side. In addition, the cantilever thickness can be easily controlled by adjusting the diffusion time, and fabricated at low cost by using bulk silicon wafers. The fabricated probe tips showed resonant frequencies of 71.420 kHz with a 1.8-µm-thick probe tip and 122.660 kHz with a 3.0-µm-thick probe tip. Using the two fabricated probe tips, we successfully demonstrate image scanning of a 1 µm grating reference sample in contact and noncontact modes, respectively.

A Hermetically-Sealed LC Resonator For Remote Pressure Monitoring

ts an integrated LC resonator structure fabricated by using bulk micromachining and anodic Igies. In this resonator structure, pressure change is monitored by a capacitive pressure sensor le change of resonance frequency. The resonance frequency shift is detected by inductive n external transmission coil; therefore, pressure can be wirelessly monitored from passive LC s been reported that intraocular pressure can be measured by passive LC resonator structure the previous structures are bulky and manually assembled in hybrid package. This is the first integrated LC resonator sensor which is hermetically sealed in a micromachined structure.