Browsing by Author "Quate, C. F."

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Open Access
Acoustic microscopy with mechanical scanning—A review
(IEEE, 1979-08) Quate, C. F.; Atalar, Abdullah; Wickramasinghe, H. K.
Acoustic waves in liquids are known to have wavelengths comparable to that of visible light if the frequency is in the gigahertz range. The phenomena of Brillouin scattering in liquids is based on such waves. In helium near 2 K acoustic waves with a wavelength of 2000 Å were studied some ten years ago at UCLA. It follows from these observations that an imaging system based on acoustic radiation with a resolving power competitive with the optical microscope is within reach if an ideal lens free from aberrations could be found. Such a lens, which was so elusive at the beginning, is now a simple device and it is the basic component in the acoustic microscope that forms the basis for this review. In this article we will establish the characteristic properties of this new instrument. We will review some of the simple properties of acoustic waves and show how a single spherical surface formed at a solid liquid interface can serve as this ideal lens free from aberrations and capable of producing diffraction limited beams. When this is incorporated into a mechanical scanning system and excited with acoustic frequencies in the microwave range images can be recorded with acoustic wavelengths equal to the wavelength of visible light. We will present images that show the elastic properties of specimens selected from the fields of material science, integrated circuits, and cell biology. The information content in these images will often exceed that of the optical micrographs. In the reflection mode we illuminate the smooth surface of a crystalline material with a highly convergent acoustic beam. The reflected field is perturbed in a unique way that is determined by the elastic properties of the reflecting surface and it shows up in the phase of the reflected acoustic field. There is a distinct and characteristic response at the output when the spacing between the object and the lens is varied. This behavior in the acoustic ieflection microscope provides a rather simple and direct means for monitoring the elastic parameters of a solid surface. It is easy to distinguish between different materials, to determine the layer thickness, and to display variations in the elastic constants on a microscopic scale. These features lead us to believe there is a promising future for the field of acoustic microscopy.
Open Access
Acoustic microscopy: resolution of subcellular detail
(National Academy of Sciences, 1979-07) Johnston, R. N.; Atalar, Abdullah; Heiserman, J.; Jipson, V.; Quate, C. F.
Recent advances now permit the use of scanning acoustic microscopy for the analysis of subcellular components. By sequential viewing of identified fixed cells with acoustic, light, and electron microscopy, we have established that the acoustic microscope can readily detect such features as nuclei and nucleoli, mitochondria, and actin cables. Under optimal conditions, images can even be obtained of filopodia, slender projections of the cell surface that are approximately 0.1-0.2 micron in diameter. Small objects separated by as little as 0.5-0.7 micron can successfully be resolved. Three aspects of the acoustic micrographs prepared in this preliminary survey seem especially prominent. These are, first, the extraordinary level of acoustic contrast that can differentiate the various cytoplasmic organelles, even in regions of very thin cytoplasm; second, the reversals in acoustic contrast that occur when altering the plane of focus; and third, the sensitivity of the acoustic response to overall cytoplasmic thickness. The acoustic microscope uses a novel source of contrast that is based on local mechanical properties. In addition, it can provide a degree of resolution that is comparable to that of the light microscope.
Open Access
Analysis and design of an interdigital cantilever as a displacement sensor
(A I P Publishing LLC, 1998-06-15) Yaralioglu, G. G.; Atalar, Abdullah; Manalis, S. R.; Quate, C. F.
The interdigital (ID) cantilever with two sets of interleaving fingers is an alternative to the conventional cantilever used in the atomic force microscope (AFM). In this paper we present a detailed analysis of the interdigital cantilever and its use as a sensor for the AFM. In this study, we combine finite element analysis with diffraction theory to simulate the mechanically induced optical response of the ID. This model is used to compare this system with the optical lever detector as used in conventional instruments by analyzing the ratio of signal to noise and overall performance. We find that optical detection of the cantilever motion with interdigital fingers has two advantages. When used in conjunction with arrays of cantilevers it is far easier to align. More importantly, it is immune to laser pointing noise and thermally excited mechanical vibrations and this improves the sensitivity as compared to the optical lever.
Open Access
Automated parallel high-speed atomic force microscopy
(A I P Publishing LLC, 1998-05-04) Minne, S. C.; Yaralioglu, G.; Manalis, S. R.; Adams, J. D.; Zesch, J.; Atalar, Abdullah; Quate, C. F.
An expandable system has been developed to operate multiple probes for the atomic force microscope in parallel at high speeds. The combined improvements from parallelism and enhanced tip speed in this system represent an increase in throughput by over two orders of magnitude. A modular cantilever design has been replicated to produce an array of 50 cantilevers with a 200 μm pitch. This design contains a dedicated integrated sensor and integrated actuator where the cells can be repeated indefinitely. Electrical shielding within the array virtually eliminates coupling between the actuators and sensors. The reduced coupling simplifies the control electronics, facilitating the design of a computer system to automate the parallel high-speed arrays. This automated system has been applied to four cantilevers within the array of 50 cantilevers, with a 20 kHz bandwidth and a noise level of less than 50 Å. For typical samples, this bandwidth allows us to scan the probes at 4 mm/s.
Open Access
Centimeter scale atomic force microscope imaging and lithography
(A I P Publishing LLC, 1998-09-21) Minne, S. C.; Adams, J. D.; Yaralioglu, G.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.
We present a 4 mm2 image taken with a parallel array of 10 cantilevers, an image spanning 6.4 mm taken with 32 cantilevers, and lithography over a 100 mm2 area using an array of 50 cantilevers. All of these results represent scan areas that are orders of magnitude larger than that of a typical atomic force microscope (0.01 mm2). Previously, the serial nature and limited scan size of the atomic force microscope prevented large scale imaging. Our design addresses these issues by using a modular micromachined parallel atomic force microscope array in conjunction with large displacement scanners. High-resolution microscopy and lithography over large areas are important for many applications, but especially in microelectronics, where integrated circuit chips typically have nanometer scale features distributed over square centimeter areas.
Open Access
Contact imaging in the atomic force microscope using a higher order flexural mode combined with a new sensor
(A I P Publishing LLC, 1996-01) Minne, S. C.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.
Using an atomic force microscope (AFM) with a silicon cantilever partially covered with a layer of zinc oxide (ZnO), we have imaged in the constant force mode by employing the ZnO as both a sensor and actuator. The cantilever deflection is determined by driving the ZnO at the second mechanical resonance while the tip is in contact with the sample. As the tip‐sample force varies, the mechanical boundary condition of the oscillating cantilever is altered, and the ZnO electrical admittance is changed. Constant force is obtained by offsetting the ZnO drive so that the admittance remains constant. We have also used the ZnO as an actuator and sensor for imaging in the intermittent contact mode. In both modes, images produced by using the ZnO as a sensor are compared to images acquired with a piezoresistive sensor.
Open Access
Dual integrated actuators for extended range high speed atomic force microscopy
(A I P Publishing LLC, 1999-09-13) Sulchek, T.; Minne, S. C.; Adams, J. D.; Fletcher, D. A.; Atalar, Abdullah; Quate, C. F.; Adderton, D. M.
A flexible system for increasing the throughput of the atomic force microscope without sacrificing imaging range is presented. The system is based on a nested feedback loop which controls a micromachined cantilever that contains both an integrated piezoelectric actuator and an integrated thermal actuator. This combination enables high speed imaging (2 mm/s) over an extended range by utilizing the piezoelectric actuator’s high bandwidth (15 kHz) and thermal actuator’s large response (300 nm/V). A constant force image, where the sample topography exceeds the range of the piezoelectric actuator alone, is presented. It has also been demonstrated that the deflection response of the thermal actuator can be linearized and controlled with an integrated diode.
Open Access
Fabrication of 100 nm pMOSFETS With Hybrid AFW / STM lithography
(IEEE, 1997-06) Soh, H. T.; Wilder, K.; Atalar, Abdullah; Quate, C. F.
Scanning probe lithography (SPL) is an emerging area of research in which the scanning tunneling microscope (STM) or atomic force microscope (AFM) is used to pattern nanometer-scale features. Four factors will dictate the viability of SPL as a patterning technology for the semiconductor industry: 1) resolution, 2) alignment accuracy, 3) reliability, and 4) throughput. We present a new SPL technique-a hybrid between the AFM and STMto address these issues. We demonstrate its capabilities and its compatibility with semiconductor processing by fabricating a pMOSFET with an effective channel length (L,ff) of 100 nm and report the device characteristics.
Open Access
High throughput, high resolution scanning probe microscopy
(Technology Publishing Ltd., 1998) Adams, J. D.; Minne, S. C.; Manalis, S. R.; Wilder, K.; Yaralioglu, G.; Atalar, Abdullah; Adderton, D.; Quate, C. F.
Open Access
High‐speed atomic force microscopy using an integrated actuator and optical lever detection
(A I P Publishing LLC, 1996-09) Manalis, S. R.; Minne, S. C.; Atalar, Abdullah; Quate, C. F.
A new procedure for high‐speed imaging with the atomic force microscope that combines an integrated ZnO piezoelectric actuator with an optical lever sensor has yielded an imaging bandwidth of 33 kHz. This bandwidth is primarily limited by a mechanical resonance of 77 kHz when the cantilever is placed in contact with a surface. Images scanned with a tip velocity of 1 cm/s have been obtained in the constant force mode by using the optical lever to measure the cantilever stress. This is accomplished by subtracting an unwanted deflection produced by the actuator from the net deflection measured by the photodiode using a linear correction circuit. We have verified that the tip/sample force is constant by monitoring the cantilever stress with an implanted piezoresistor.
Open Access
High-speed tapping mode imaging with active Q control for atomic force microscopy
(American Institute of Physics, 2000) Sulchek, T.; Hsieh, R.; Adams, J. D.; Yaralioglu, G. G.; Minne, S. C.; Quate, C. F.; Cleveland, J. P.; Atalar, Abdullah; Adderton, D. M.
The speed of tapping mode imaging with the atomic force microscope(AFM) has been increased by over an order of magnitude. The enhanced operation is achieved by (1) increasing the instrument’s mechanical bandwidth and (2) actively controlling the cantilever’s dynamics. The instrument’s mechanical bandwidth is increased by an order of magnitude by replacing the piezotube z-axis actuator with an integrated zinc oxide (ZnO)piezoelectric cantilever. The cantilever’s dynamics are optimized for high-speed operation by actively damping the quality factor (Q) of the cantilever. Active damping allows the amplitude of the oscillating cantilever to respond to topography changes more quickly. With these two advancements, 80μm×80 μm high-speed tapping mode images have been obtained with a scan frequency of 15 Hz. This corresponds to a tip velocity of 2.4 mm/s.
Open Access
Hybrid atomic force/scanning tunneling lithography
(American Vacuum Society, 1997) Wilder, K.; Soh, H. T.; Atalar, Abdullah; Quate, C. F.
We present a new technique for performing lithography with scanning probes that has several advantages over standard methods. This hybrid lithography system combines the key features of the atomic force microscope (AFM) and the scanning tunneling microscope (STM) by incorporating two independent feedback loops, one to control current and one to control force. We demonstrate a minimum resolution of 41 nm and nanometer alignment capabilities. This lithography system is capable of writing continuous features over sample topography. Topography is often present in real patterning applications and poses problems for AFM and STM lithography. We report 100 nm resist features patterned over 180 nm of topography created by local oxidation of silicon. The hybrid AFM/STM system is designed as a robust scanning probe lithography tool, capable of high-speed patterning and suited for integrated circuit lithography applications.
Open Access
Independent parallel lithography using the atomic force microscope
(A I P Publishing LLC, 1996-05) Minne, S. C.; Manalis, S. R.; Atalar, Abdullah; Quate, C. F.
Independent parallel features have been lithographically patterned with a 2×1 array of individually controlled cantilevers using an atomic force microscope. Control of the individual cantilevers was achieved with an integrated piezoelectric actuator in feedback with a piezoresistive sensor. Patterns were formed on 〈100〉 single crystal silicon by using a computer controlled tip voltage to locally enhance the oxidation of the silicon. Using the piezoresistor directly as a force sensor, parallel images can be simultaneously acquired in the constant force mode. A discussion of electrostatic forces due to applied tip voltages, hysteresis characteristics of the actuator, and the cantilever system is also presented.
Open Access
Integration of through-wafer interconnects with a two-dimensional cantilever array
(Elsevier, 2000-05-22) Chow, E. M.; Soh, H. T.; Lee, H. C.; Adams, J. D.; Minne, S. C.; Yaralioglu, G. G.; Atalar, Abdullah; Quate, C. F.; Kenny, T. W.
High-density through-wafer interconnects are incorporated in a two-dimensional (2D) micromachined cantilever array. The design addresses alignment and density issues associated with 2D arrays. Each cantilever has piezoresistive deflection sensors and high-aspect ratio silicon tips. The fabrication process and array operation are described. The integration of cantilevers, tips, and interconnects enables operation of a high-density 2D scanning probe array over large areas.
Open Access
Interdigital cantilevers for atomic force microscopy
(A I P Publishing LLC, 1996-10) Manalis, S. R.; Minne, S. C.; Atalar, Abdullah; Quate, C. F.
We present a sensor for the atomic force microscope (AFM) where a silicon cantilever is micromachined into the shape of interdigitated fingers that form a diffraction grating. When detecting a force, alternating fingers are displaced while remaining fingers are held fixed. This creates a phase sensitive diffraction grating, allowing the cantilever displacement to be determined by measuring the intensity of diffracted modes. This cantilever can be used with a standard AFM without modification while achieving the sensitivity of the interferometer and maintaining the simplicity of the optical lever. Since optical interference occurs between alternating fingers that are fabricated on the cantilever, laser intensity rather than position can be measured by crudely positioning a photodiode. We estimate that the rms noise of this sensor in a 10 hz–1 kHz bandwidth is ∼0.02 Å and present images of graphite with atomic resolution.
Open Access
Nanometer-scale patterning and individual current-controlled lithography using multiple scanning probes
(A I P Publishing LLC, 1999-06) Wilder, K.; Soh, H. T.; Atalar, Abdullah; Quate, C. F.
Scanning probe lithography (SPL) is capable of sub-30-nm-patterning resolution and nanometer-scale alignment registration, suggesting it might provide a solution to the semiconductor industry’s lithography challenges. However, SPL throughput is significantly lower than conventional lithography techniques. Low throughput most limits the widespread use of SPL for high resolution patterning applications. This article addresses the speed constraints for reliable patterning of organic resists. Electrons field emitted from a sharp probe tip are used to expose the resist. Finite tip-sample capacitance limits the bandwidth of current-controlled lithography in which the tip-sample voltage bias is varied to maintain a fixed emission current during exposure. We have introduced a capacitance compensation scheme to ensure continuous resist exposure of SAL601 polymer resist at scan speeds up to 1 mm/s. We also demonstrate parallel resist exposure with two tips, where the emission current from each tip is individually controlled. Simultaneous patterning with multiple tips may make SPL a viable technology for high resolution lithography.
Open Access
Parallel atomic force microscopy with optical interferometric detection
(American Institute of Physics, 2001-01-05) Sulchek, T.; Grow, R. J.; Yaralioglu, G. G.; Minne, S. C.; Quate, C. F.; Manalis, S. R.; Kiraz, A.; Aydine, A.; Atalar, Abdullah
We have developed an atomic force microscope that uses interferometry for parallel readout of a cantilever array. Each cantilever contains a phase sensitive diffraction grating consisting of a reference and movable set of interdigitated fingers. As a force is applied to the tip, the movable set is displaced and the intensity of the diffracted orders is altered. The order intensity from each cantilever is measured with a custom array of siliconphotodiodes with integrated complementary metal–oxide–semiconductor amplifiers. We present images from five cantilevers acquired in the constant height mode that reveal surface features 2 nm in height. The interdigital method for cantilever array readout is scalable, provides angstrom resolution, and is potentially simpler to implement than other methods. © 2001 American Institute of Physics
Open Access
Phase imaging in reflection with the acoustic microscope
(A I P Publishing, 1978-01) Atalar, Abdullah; Quate, C. F.; Wickramasinghe, H. K.
When a polished surface of a single crystal is examined with a converging acoustic beam the reflected signal has a characteristic response that is dependent upon the elastic properties of the reflecting surface. This property can be used in the acoustic microscope to monitor the thickness of layers deposited on these surfaces and the small‐scale variations of the elastic parameters in these materials.
Open Access
Resonant harmonic response in tapping-mode atomic force microscopy
(American Physical Society, 2004) Sahin, O.; Quate, C. F.; Solgaard, O.; Atalar, Abdullah
Higher harmonics in tapping-mode atomic force microscopy offers the potential for imaging and sensing material properties at the nanoscale. The signal level at a given harmonic of the fundamental mode can be enhanced if the cantilever is designed in such a way that the frequency of one of the higher harmonics of the fundamental mode (designated as the resonant harmonic) matches the resonant frequency of a higher-order flexural mode. Here we present an analytical approach that relates the amplitude and phase of the cantilever vibration at the frequency of the resonant harmonic to the elastic modulus of the sample. The resonant harmonic response is optimized for different samples with a proper design of the cantilever. It is found that resonant harmonics are sensitive to the stiffness of the material under investigation.
Open Access
Silicon micromachined ultrasonic immersion transducers
(A I P Publishing LLC, 1996-12-09) Soh, H. T.; Ladabaum, I.; Atalar, Abdullah; Quate, C. F.; Khuri-Yakub, B. T.
Broadband transmission of ultrasound in water using capacitive, micromachined transducers is reported. Transmission experiments using the same pair of devices at 4, 6, and 8 MHz with a signal‐to‐noise ratio greater than 48 dB are presented. Transmission is observed from 1 to 20 MHz. Better receiving electronics are necessary to demonstrate operation beyond this range. Furthermore, the same pair of transducers is operated at resonance to demonstrate ultrasound transmission in air at 6 MHz. The versatile transducers are made using siliconsurfacemicromachining techniques. Computer simulations confirm the experimental results and are used to show that this technology promises to yield immersion transducers that are competitive with piezoelectric devices in terms of performance, enabling systems with 130 dB dynamic range. The advantage of the micromachined transducers is that they can be operated in high‐temperature environments and that arrays can be fabricated at lower cost.