N. Sarkar

Microassembled tunable MEMS inductor

In this work we present a heterogeneous microassembly consisting of a MEMS translation stage, a copper electroplated solenoid inductor, and a ferromagnetic NiFe core, integrated on a Pyrex sub-mount. The system was assembled by a 5 degree-of-freedom automated motion control platform using hybrid MEMS assembly technology and a design library of silicon microgrippers, sockets and handles. The tunable inductor was characterized using various core materials from 300 kHz to 20 GHz and has a self-resonant frequency (SRF) of 10 GHz, a Q over 50, and inductance values from 5.5 to 40 nH over its useful frequency range. A nanomagnetic composite material containing Co/sub 83.2/B/sub 3.3/Si/sub 5.9/Mn/sub 7.6/ exhibited continuous enhancement in inductance and Q up to the self-resonant frequency of the device. The device operates on 7 volts and consumes no quiescent power once it is tuned, due to the power-off engage mechanism incorporated in the translation stage.

Single-Chip CMOS-MEMS Dual Mode Scanning Microwave Microscope

We present the design, fabrication and experimental validation of an integrated Scanning Microwave Microscopy (SMM)/Atomic Force Microscopy (AFM) system that does not require the use of a conventional laser-based AFM. Microfabricated SMM probes are collocated with piezoresistive strain-based sensing AFM probes in a CMOS-MEMS process, and are actuated by integrated electrothermal scanners. Integration of AFM enables dual mode imaging (topography and electrical properties) and more importantly, it enables control over tip-sample distance, which is crucial for accurate SMM imaging. This design is unique in the sense that the tip can be scanned over the sample in 3 degrees of freedom, over a 20 μm×10 μm×30 μm scan range in the x, y, and z directions respectively. We fabricate our device by using a standard foundry CMOS process followed by in-house maskless MEMS post processing to release the devices. Single-chip SMM/AFM devices with integrated 1-D and 3-D actuation are thus obtained. These devices can be used to modulate the tip-sample separation to underlying samples with a periodic signal, improving immunity to long-term system drifts. We also investigate the effect of tip-sample separation on the resolution of the instrument. To increase measurement sensitivity, a single-stub matching network has been used to match the high tip-to-sample impedance to the 50 ohm characteristic impedance of a performance network analyzer. Measurement results of the CMOS-MEMS SMM are presented to verify the proposed concept.

Self-actuating scanning microwave microscopy probes

We present the design and experimental results of a scanning microwave microscopy (SMM) system that does not require the use of a conventional atomic force microscope (AFM). Microfabricated SMM probes are actuated by integrated MEMS scanners in a commercially available multi-user process. This design is unique in the sense that the tip can be scanned over the sample both laterally and vertically, over a 10µm × 10µm scan range. We first validate our approach with a test-bench consisting of a fixed probe and an integrated sample-scanning stage. This device is used to obtain characteristic approach curves of S11 as a function of tip-sample separation. We then investigate the effect of tip-sample separation on the resolution of the instrument. CPW probes with integrated 1-D and 2-D actuation are then presented. These devices can be used to modulate the tip-sample separation to off-chip samples with a periodic (200Hz) signal, improving immunity to long-term system drifts. To increase measurement sensitivity, a single-stub matching network has been used to match high tip to sample impedance to the 50 ohm of a performance network analyzer. Measurement results agree very well with reported SMM measurements in the literature

A 0.25mm 3 Atomic Force Microscope on-a-chip

This paper reports the highest resolution achieved with a single-chip Atomic Force Microscope (sc-AFM). Images of a 20nm AFM calibration standard were obtained to show, for the first time, that single-chip instruments may obtain a vertical resolution comparable to state-of-the-art instruments at a minuscule fraction of the size (volume=1/1,000,000) and cost (1/1000). A maskless, 2-step release process is performed on CMOS chips in order to obtain devices that can image a sample without the need for any off-chip scanning or sensing components. We report a four-fold improvement in resolution when compared to previously reported sc-AFMs, enabling metrology for nanoscale manufacturing using MEMS AFM technology.

Single-chip atomic force microscope with integrated Q-enhancement and isothermal scanning

We present the highest resolution imaging performance attained to date with a single-chip Atomic Force Microscope (AFM) that does not require off-chip scanning or sensing hardware. The marked improvement in sensitivity of the instrument stems in part from an internal quality (Q) factor enhancement mechanism that relies on the interplay between effects in the electrical, thermal and mechanical domains. In addition, careful matching of the strain sensor in an electrothermally actuated, piezoresistively detected resonant cantilever improves the dynamic range of the instrument. Furthermore, an integrated isothermal electrothermal scanner has been developed to scan a surface area of ~50μm × ~15μm while maintaining a constant temperature at the tip and sensor locations, thereby suppressing the deleterious thermal crosstalk effects that have plagued previously reported electrothermal scanner designs.

A distortion-free single-chip atomic force microscope with 2DOF isothermal scanning

A distortion free single-chip scanning probe microscope (sc-SPM) has been developed. The reported design integrates the 3 DOF scanner, sensors, and tip that are required for nanometer-scale measurements onto a single chip. This low-cost instrument has achieved imaging resolution comparable to conventional tools without the image distortion that was present in prior single-chip SPMs, arising from thermal coupling between electrothermal actuators. A single chip atomic force microscope is used with a novel 2D isothermal scanning algorithm to obtain a 5 μm × 3 μm rectangular topographical map, free from image distortion.

A multimode single-chip scanning probe microscope for simultaneous topographical and thermal metrology at the nanometer scale

This paper reports the first single-chip scanning probe microscope (sc-SPM) that is capable of simultaneously performing atomic force microscopy (AFM) and scanning thermal microscopy (SThM) without requiring any off-chip scanning or sensing components. A thermal-piezoresistive resonant sensor is used to hold the tip-sample interaction force constant, while a bolometer-style probe measures local heat transfer effects. The reported instrument obtains local thermal measurements of powered electrothermal MEMS devices and also achieves the first patterning results with a single-chip scanning probe instrument. Importantly, subsurface features on a 22nm CMOS chip are revealed by thermal phase imaging with the present device.

Optical MEMS index finger microgesture input sensor for mobile and wearable devices

We report the first optical microsystem that captures index finger microgestures with the precision, bandwidth, power consumption and form-factor required for close-range handwriting and gesture keyboarding (e.g. Swipe) on smart watches and mobile handsets. Finger position is measured with 30μm resolution (at a 5cm distance) at a bandwidth of up to 550Hz while consuming less than 15mW with the reported prototype system. A VCSEL, scanning diffractive optic element (DOE), and photodiode may be packaged in a 2×2×1mm package to fit unobtrusively in a wearable device. This component may enable the first information-rich touch-less gesture inputs to wearables.

A platform technology for metrology, manipulation and automation at the nanoscale

We present a platform technology for nanometer-scale metrology, manipulation, automation and robotics that consists of ultra-precise actuators, sensors, and electronics on a single CMOS chip. A conventional CMOS process is adopted to manufacture MEMS devices that can position payloads with sub-nanometer resolution and dynamically detect forces in the piconewton range. One example of an aggressively scaled device that has been designed, fabricated, characterized and commercialized in the present platform is a single-chip atomic force microscope (sc-AFM) that achieves atomic lattice resolution in the vertical direction. The modeling and design of sc-AFMs to optimize their distortion-free scan range, speed of operation, and robustness to ambient fluctuations are presented as example applications of the CMOS-MEMS technology platform.

High Speed, Large Scan Area, Distortion Free Operation of a Single-Chip Scanning Probe Microscope

Despite the exquisite resolution that may be obtained with AFMs, the industrial nanometrology enterprise has been reluctant to include them in their suite of inspection tools. The single-chip AFM [1] was introduced to overcome several shortcomings of conventional AFMs by replacing bulky piezoelectric scanners with 3 degree-of-freedom electrothermal (ET) MEMS actuators and by replacing laser detection with thermal-piezoresistive resonant sensing. These single-chip instruments are wellsuited to high-speed operation and may also be implemented as arrays, as they include all of the components that are required for an AFM to obtain an image on a single chip.