METAL AND SEMIMETAL SENSORS NEAR THE METAL INSULATOR TRANSITION REGIME
This invention generally relates to sensors made of granular thin films in the discontinuous phase. More particularly, the invention relates to microbolometers and displacement sensors fabricated from thin films that are close to the metal insulator transition (MIT) or metal semiconductor transition (MST) regime. Sensors of various designs have been fabricated according to the invention and may be used for deflection measurements, nano-indentation, visco-elastic measurements, topographical scanning, explosive detection, low abundance biomolecular detection, electromagnetic radiation detection and other similar detection and measurement systems.
This invention generally relates to sensors made of granular metallic or semimetallic thin films in the discontinuous phase. More particularly, the invention relates to uncooled microbolometers and displacement sensors fabricated from thin films that are close to the metal insulator transition (MIT) or metal semiconductor transition (MST) regime.BACKGROUND OF THE INVENTION
Monitoring devices with embedded infrared sensors and detectors are frequently used for video surveillance of people and premises, fire detection, emergency responses, and various other applications where there is a need for such sensors and detectors. Detectors generally operate by detecting the differences in the thermal radiance of various objects in a particular scene. These differences in thermal radiation are converted into electrical signals which are processed, analyzed, and displayed as images in the case of video imager's and noise signals for detectors.
The use of bolometers as infrared detectors and imagers are well known in the art. In many cases the sensor array is a microbolometer array. When a microbolometer array absorbs infrared radiation of objects and their surroundings, there is a corresponding change in electrical resistance generated by a change in the microbolometer temperature. When used as an infrared detector or imager, the change in electrical resistance of the bolometer material resulting from the temperature change due to absorption of infrared radiation, is measured and recorded. Bolometers and microbolometers therefore generally act as resistive thermometers.
Cooled microbolometer detectors are costly to fabricate, heavier in weight, have shorter lifetimes, low yields, and consume considerably more power than uncooled microbolometers. Besides being lighter in weight, the uncooled microbolometers are cheaper to fabricate and consume less power than the cooled microbolometers. Uncooled microbolometers are currently used in the manufacture of highly specialized thermal imaging applications such as night vision and Scanning Thermal Microscopy (SThM) [1, 2, 3]. Two types of SThM microbolometers have shown considerable promise: Doped silicon microbolometers with temperature coefficient of resistance (TCR) between 0.003/K and 0.0056/K that are integrated into single-crystal silicon cantilevers [10, 11], and metallic microbolometers with a TCR around 0.0029/K .
The effective operation of microbolometers as infrared sensors and detectors requires them to have a high temperature coefficient of resistance (TCR) and low noise characteristics. The temperature coefficient of resistance (TCR) or a is the ratio of increased conductor resistance per degree Celsius rise in temperature of the conductor material. A material with a large value of TCR provides the best sensing capability. A higher sensitivity material is required to achieve the larger values of TCR. With pure metals, the TCR is a positive number because the resistance of these metals increases with increasing temperatures. Therefore, when bolometers and more particularly, microbolometers are used as infrared imagers to measure electromagnetic radiation emitted by surrounding objects, the efficiency of these imagers depend to a large extent on the metal used in the imagers. Lower resistivity bolometer film materials often have lower TCR values.
Microbolometers are generally fabricated on a substrate material using integrated circuit fabrication techniques. Adequate signal-to-noise ratio is essential for image processing and display. The signal to noise ratio as well as the response time and sensitivity of the bolometer depends on the thermal mass and thermal isolation from the supporting structure. The response time of a microbolometer is the time required for a detector to absorb sufficient infrared radiation to change the electrical resistance of the detector element accompanied by the dissipation of heat generated by the absorption of the infrared radiation. Microbolometer sensitivity on the other hand is determined by the amount of infrared radiation necessary to cause sufficient change in the electrical property of the microbolometer detector. With increase in thermal mass there is a decrease in sensitivity and increase in response time. Therefore, the thicker, the bolometer film material, the poorer, the overall performance of the imager.
The common semiconductor materials used in microbolometers are vanadium oxide (VOx), amorphous silicon (a-Si), and titanium oxide (TiOx). Some of the earlier bolometers used vanadium oxide as the semiconductor material (U.S. Pat. No. 5,450,053). Vanadium oxide has a TCR of approximately, 0.05/K and a superior noise equivalent temperature difference (NETD). However, vanadium oxide introduces a significant number of deposition problems [6,7,8]. U.S. Pat. No. 6,836,677 discloses a bolometer with a TCR higher than the conventional bolometers. The bolometer according to this disclosure uses a thin film of a crystalline or polycrystalline oxide selected from alkaline and rare earth elements, and one or more elements belonging to Period 5 or Period 6 of the Periodic Table. Polycrystalline and amorphous silicon have a high TCR of up to 0.05/K, but exhibit adverse noise characteristics [4,5,6]. In addition, microbolometers fabricated from vanadium oxides (VOx) and amorphous silicon (a-Si) have been shown to exhibit permanent changes in their electrical properties and in some cases mechanical deformation with a rise in temperature, even if temporary, resulting in changes in TCR values. The use of pure titanium and its alloys result in a bolometer that occupies a significant amount of space as described in U.S. Pat. No. 5,698,852. U.S. Pat. No. 7,442,933 discloses a bolometer that has substantially high resistance stability and substantially low 1/F noise. The bolometer in this patent comprises a substrate and a TiOx layer formed over the substrate, where the x value of the TiOx layer is in the range of 1.68 to 1.95.
Microbolometers have to be fabricated at temperatures compatible with Complementary Metal-Oxide-Semiconductor (CMOS) technology. In addition, the materials used to manufacture microbolometers must be inexpensive and compatible with current CMOS processes. Thin film metallic microbolometers have very low noise characteristics in addition to a low TCR of 0.005/K [6,9]. Thin film metallic microbolometers have other important advantages as well, including, simplified fabrication and a lower manufacturing cost. Metallic microbolometers also enable the use of alternative substrate materials such as polymers that tend to exhibit higher compliance properties and improved thermal isolation for better temperature resolution. U.S. Pat. No. 7,527,999 discloses the manufacture of a microbolometer film material Cd1-xZnxS, with a TCR in the value ranges from 1.5% to 3.7% for use at temperatures compatible with CMOS technology.
As a metal film is being deposited, the electrical properties of granular metals vary continuously as the composition of metal and non-metal mixtures is changed . Metal deposition goes through the following four phases before it starts behaving like a bulk film. The first phase is nucleation which is the clustering of atoms and molecules. During nucleation, the film is highly susceptible to environmental and deposition conditions and substrate surface conditions. The second phase is island formation where stable nuclei grow and appropriate other nuclei. The third phase is when the islands combine to form networks of a few islands in contact with each other. This phase along with the first two phases are considered discontinuous. Finally, the film becomes continuous, but porous as some channels between the networks get filled [14-17]. Typically, island films have negative TCR while porous films have a positive TCR like bulk materials. The TCR for porous films is lower than that of thick bulk film [14, 15, 18, 19, 20]. Unlike bulk films, ultrathin films are comprised of a series of metal islands or grains, rather than a continuous film. The transport between films is due to tunneling or hopping. A small change in distance between the grains due to bending, results in a large change in resistance of the film. Accordingly, the gauge factor of these films is higher. In the present invention, cantilever sensors for sensing bending include metal sensors based on discontinuous films.
The primary conditions that have to be met as part of the continuing effort to develop, smaller, better performing microbolometers that weigh less and consume less power are, high temperature coefficient of resistance (TCR), low noise, inexpensive material, and compatibility with current Complementary Metal-Oxide-Semiconductor (CMOS) processes. The microbolometer of the present invention is fabricated taking into consideration these conditions and fills the deficiency gap for these conditions in the prior art.
An object of the present invention is to present the design of suspended beam sensors made of granular metallic, metal oxides such as, indium oxide, tin oxide, zinc oxide, or semimetallic thin films in the discontinuous phase. These sensors are used either as bolometers or as displacement sensors for sensing movement. Another object of the present invention is to present fabrication methods for these sensors from thin films that are close to the metal insulator transition (MIT) regime.SUMMARY OF THE INVENTION
This invention generally relates to sensors made of granular metallic or semimetallic thin film in the discontinuous phase. More particularly, the invention relates to uncooled microbolometers and displacement sensors fabricated from thin films that are close to the metal insulator transition (MIT) or the metal semiconductor transition (MST) regime. In this disclosure the MIT regime and thickness are defined as the thickness where the I-V curve crosses over from sublinear to superlinear, and TCR transitions from positive to negative. Therefore, near the MIT regime there is a zero value of TCR and a high negative value of TCR both of which are of interest. The gauge factor for sensing displacement is also very large.
In one embodiment, intended for scanning thermal microscopy (SThM), an ultrathin film (<20 nm) titanium microbolometer integrated onto a SiO2/Si3N4/SiO2 (ONO) cantilever with a Si/SiO2 tip has been fabricated. Wafers with different thicknesses of titanium were also prepared and tested. The morphology of these metal thin films (discontinuous form versus continuous form)  is revealed by measuring their electrical properties and atomic force microscopy imaging. Titanium thin film properties near the MIT regime improve the sensitivity of metal microbolometers. Sheet resistances corresponding to the highest TCR and the lowest TCR, in absolute values have been determined. The relationship between TCR and resistance may be typical for many metal, metal oxides, and semimetal thin films near room temperatures. Applications of metal, metal oxides or semimetal films with resistance thicknesses near the MIT can be extended to infrared imaging and chemical sensing. Another object of this invention is to present the design of suspended beam sensors made of granular metallic or semimetallic thin film in the discontinuous phase. These sensors are used either as bolometers or as sensors for sensing movement.
These and other features of the present invention will become obvious to one skilled in the art through the description of the drawings, detailed description of the invention, and the appended claims.
The object of the present invention is to provide a method for fabrication of an uncooled microbolometer from thin films of metals and semimetals close to the metal insulator transition (MIT) regime and/or near the metal semiconductor transition (MST) regime. Another object of the present invention is to fabricate a microbolometer that attains the maximum temperature coefficient of resistance (TCR) near the metal insulator transition (MIT) regime. Yet, another object of the invention is to present the design of suspended beam sensors made of granular metallic or semimetallic thin film in the discontinuous phase. These sensors are used either as bolometers or as displacement sensors.
Referring now to the drawings, more particularly to
R(T)/R(300K.) correspond to resistors on a wafer with sheet resistances of 0.29 kΩ/, and 6.4 kΩ/, and microbolometers with sheet resistances of 11.6 kΩ/ and 74.9 kΩ/. It can be observed that as the resistance increases, the slope of the sheet resistance vs. temperature changes from positive to negative. With increasing sheet resistance, the TCR values first shift from positive to negative and then continue to decrease until they plateau (after a specific resistance value). There is an optimal sheet resistance beyond which there is no improvement in bolometric sensitivity. For the titanium films studied, this value was measured to be at approximately 74.9 kΩ/ with a minimum TCR value of around −6790 ppm/K.
Another sheet resistance value of interest is near 1 kΩ/ where the TCR is close to zero. This is useful for applications that require resistors that are not influenced by temperature fluctuations. These two results may be combined in order to develop microbolometers where the sensing area would be of a thickness that would provide the highest TCR in absolute values, while the electrodes would be of a thickness near zero TCR. Similar to the crossover from sublinear to superlinear I-V characteristics, the transition from positive to negative TCR also occurs at around 1 kΩ/.
Optionally, a layer may be deposited on top of the metal to insulate the material or for other purposes such as to provide protection. That sandwich layer may be of any of the materials mentioned above including polymers, elastomers, silicon nitride, etc. Any other prior art process can be used. The cantilever can be a suspended beam with one or two anchors. The beam can be made of any of the following materials: SU8, polymers, silicon nitride, oxide, silicon oxide, silicon or a combination thereof. In order to increase the thermal isolation of the sensor, the beam needs to be very thin. The metal or semimetal used for a sensing element can be any metal with thickness near the metal insulator transition (MIT) region. The sensing area may remain exposed while the rest of the area may be made of any other conducting material. This process may be used to fabricate a cantilever or a suspended beam with two anchors. In order to increase sensitivity at the sensing area, following the granular thin film deposition, a second metal layer may be deposited with openings in the sensing area(s) making these areas more susceptible to temperature changes or bending or other types of changes.
In all these processes, optionally, the top and bottom cantilever material can form a sandwich with the sensing element in the middle by depositing cantilever material on both sides. Forming a tip is also optional. Finally, oxide sharpening of the tip is optional.
These devices can also be used for the thermal tapping mode of Atomic Force Microscopes (AFM) scanning or in mass measurements, for instance, in chemical detection or biological applications. The cantilevers oscillate by the thermal bimorph effect of the metal cantilever. The device employs a resistive heater. This can be used with an AFM or without an AFM. A function generator and a lock-in amplifier can be used. A function generator is used to apply sinusoidal alternating current ac to the probe's thin film resistor. Ac driven intermittent heating and cooling causes the cantilever to vibrate due to the bimorph effect. An AFM laser aligned on the cantilever is reflected into the photodetector and can be used to measure the amplitude changes. The sample is scanned without the optomechanical feedback. The deflection signal provides topographical information, while the amplitude of the oscillation is related to the damping of the tip-sample interaction, and provides parametric information.
The thermal sensor is designed so that most of the change in resistance occurs at the desired sensing area. This can be achieved by making the rest of the metal line wider and thicker and even depositing a second layer of metal over the metal line excluding the sensing area. Sometimes the above strategies are not enough to reduce the noise from the metal lines. As a result, the signal from the sensing area 804 is not as clear. A reference cantilever has been used as one of the four resistors in a Wheatstone bridge arrangement to overcome this. In this disclosure described in
Displacement and Mass Measurement
For a bulk material, piezoresistivity is the coupling between the stress tensor and the electrical resistivity, represented by the equation:
Here σ is the stress tensor p is the change in resistivity tensor. For metals, the piezoresistive effect is mainly due to smaller mean free path from smaller lattice spacing. For semiconductors, there is an additional effect due to change in curvature of the E-k diagram resulting in change in effective electron mass. In certain cases (like 44piezoresistivity) the enhanced piezo-resistive effect is due to change in relative separation of different bands, which facilitate the interband movement of electrons due to change in crystal structure. U.S. Pat. No. 7,249,859 discloses the use of bimaterial piezoresistive cantilevers with metals such as, Au—Si, Pd—Si, Au—Si3N4, and Pd—Si3N4 as an actuating and sensing element. U.S. Pat. Appl. No. 20030089182 also discloses bimaterial piezoresistive cantilevers with metal as an actuating and sensing element. In most cases actuation of the cantilever occurs due to the bimaterial effect—when two materials with different expansion coefficients are used on a cantilever. When one of the materials is heated periodically, it expands and contracts while the second material is not heated, causing the beam to vibrate.
In the present invention, resistivity at the metal-insulator transition for heterogeneously disordered thin films is given by ρc=A(h/e2)d, where A ˜1 and d is the average grain size, ρc corresponds to R=10 kOhm/. Metal-insulator transition (MIT) is observed between the TCR ranges. This behavior can be explained by dividing the TCR range into three distinct regions: a) Near 0, where there is a balance between weak localization effects and Boltzmann behavior, b) low negative TCR values region that can be explained by weak localization, and c) TCR ranges at very high negative TCR values which usually are described by variable range hopping.
As the probe is scanned across the sample, the bridge, which was initially balanced, will be unbalanced because the probe resistance changes. The error voltage V+−V− across the two nodes of the bridge is amplified and fed to a PC that runs the software for reconstructing the image or profile of the sample. The signal goes through the first gain stage (where it is amplified by ×100), then through a low pass filter, and then through a second gain stage (where it is amplified by either ×10 or ×100), finally the signal goes through a buffer.
Single Cell Elastography and Viscoelastic Material Properties
Research has shown that a large number of diseases such as osteoporosis, osteoarthritis, cystic fibrosis, muscular dystrophy, ventricular aneurysm, cancer, cirrhosis of the liver etc. exhibit abnormal tissue biomechanics . There is a fast growing clinical interest in the ability to diagnose disease based on analysis of tissue mechanical properties. A number of indentation devices that have achieved minor clinical acceptance evaluate the stiffness of tissues quantitatively. Chief among them is the elastogram. An elastogram provides new information not available using conventional medical imaging methods because the image is constructed from regional differences of tissue responding to applied loads.
Atomic Force Microscopes (AFM) have been widely used as nano-indenters to measure the viscoelastic material properties of living cells in culture. With AFM elastography the structure and function of the underlying cell's cytoskeleton is examined from a map of the cell's mechanical properties which is produced by combining imaging and indentation. Although indentation experiments with AFM are very common, it is necessary to develop more sophisticated tests completely characterize cell properties.
Almost all physical, chemical and biological processes have an associated heat effect. The enabling technology proposed in the present invention provides a sensitive non-destructive diagnostic method to determine where and how much heat was exchanged following a physical or chemical process. The scanning deflection measurement probe disclosed in this invention can be used to research biological activity and structures both on the cell membrane and inside the cell. The scanning probe can facilitate studies relating to cancer and carcinogenic research. A critical application of the instrument is in understanding the biological basis of cancer at the cellular level by utilizing tumor cells and tissues to analyze the mechanisms responsible for the growth and progression of cancer.
Recent events have exposed the urgent demand for reliable and inexpensive systems for remote detection of explosives. Among different explosives, plastic explosives such as PETN and RDX are the most difficult to detect because of their low vapor pressures. The difficulty is further aggravated for stand-off detection, as the concentration in the ambient air is even lower. Moreover, the detection has to be rapid enough to take at most a few seconds, when the false positives are limited. The device should be able to simultaneously detect different kinds of explosives, while operating in a field where both temperatures and chemical environment may vary significantly.
Recently, there has been considerable work in the area of microfabricated chemical sensors and systems for trace explosives detection. These microsystems can potentially enable low-cost and reliable handheld systems for explosive detection or wireless explosive sensing network for cargos, buildings and other security purposes. Among the many different techniques, film based sensor arrays are commonly used for chemical detection. The structures of these sensor arrays are usually microfabricated nano-cantilevers that are coated with different sensor materials. When the sensing materials selectively adsorb the target chemicals, the mechanical characteristics of the nano-cantilevers such as bending, stress mass, and resonant frequency will change and can be detected with various methods. This technique can provide simultaneous rapid detection for various explosives at the fraction of the cost. In addition, this cantilever based detection is very promising due to its inherently high sensitivity and ease of fabrication and integration. The sensors are simple enough to be fabricated in a low-cost process and consequently have great potential to be implemented to a wireless explosive sensing network for explosive monitoring. Furthermore, the growth of Atomic Force Microscopy (AFM) technology has enabled the development of micro-cantilevers whose bending can be detected in exquisite resolutions.
Among the various kinds of cantilever sensors, devices made from polymeric material show the greatest sensitivity. The sensitivity of a piezoresistive cantilever is given by the equation:
where K is the gauge factor, E is the Young's modulus, s is the uniform surface stress on the cantilever. The gauge factor for ultrathin films of gold (<10 nm thick) has been reported to be between, 24-48 [Li94]. Silicon nitride (Si3N4) and silicon are the common materials for micro and nanocantilevers. While the Young's moduli of silicon nitride and silicon are 180 GPa and 110 GPa, respectively, polyimide has a Young's modulus of 7.5 GPa and parylene has a Young's Modulus of 4 GPa. Piezoresistive microcantilevers provide an excellent platform for inexpensive and portable trace detection of explosives. Advantages include high sensitivity and linearity, ease of fabrication and calibration and good scalability to a multi-probe array and can be used for both static and dynamic measurements. Additionally, the piezoresistive measurement can be applied in different environments including in air and liquids, at low and high temperatures (−35° C.-200° C.) and does not require an ultraclean environment.
Nanocantilevers which can measure chemisorption down to 1 ag, and have a noise limited displacement sensitivity of 39 fm Hz-½ at atmospheric pressure have been demonstrated [Rou06]. While these results are excellent, it is possible to improve sensitivity further by using this polymer cantilever technology. The embodiment of the present invention embeds a sensor on a micro or nanocantilever that is made of an ultracompliant material such as polyimide or paralyne in order to measure the variation of the surface strain of the defected cantilever. This process is particularly suitable for mass production for sensor arrays. The use of arrays allows compensations for environmental changes and non-specific binding, consequently reduces false positives and provides a greater dynamic range.Biomolecular Detection
Existing technologies such as ELISA and surface plasmon resonance spectroscopy (SPR) are inefficient in detecting the low abundance components in a mixture. These low abundance components may provide important information about the status of a cell. Small changes of concentration or altered modification patterns of disease-relevant low abundance components can be potentially used as markers of different stages of cancer, in diagnosis, in monitoring the growth of the tumor, and response to the therapy. Many disease biomarkers exist in the body in a very low concentration. Low-copy-number proteins (<1000 molecules/cell) have a significant function in cell operation, including signaling and regulation of gene expression. Their abundance is far below the sensitivity limits of current analysis methods.
Prior cantilever work has demonstrated the capability of detecting biomolecules with the cantilever sensors. However, the present invention aims at, a) advancing the sensing limits to detect low abundance biomolecules (×10 higher sensitivity than the existing cantilevers), b) shrinking the size of cantilevers to smaller than 1 micron dimensions in order to detect a small number of molecules. An embodiment of the present invention can be used for the detection of low abundance biomolecules using an array of nano-cantilevers made of parylene with embedded sensors on a microfluidic chip. The cantilevers are coated with the desired receptors to bind proteins, peptides or micro RNAs. Several innovations are included in this embodiment, including: 1) use of parylene to fabricate the cantilevers with at least ×10 higher sensitivity, 2) reduction of cantilever size to nanometer dimensions uniquely enabled by our proprietary fabrication techniques, 3) ultra thin metallic piezoresistive films increase sensitivity and eliminate the need of the atomic force microscopy (AFM) optical detection system, 4) address non-specific binding using a combination of strategies simultaneously. A massively parallel system for performing assays can be developed. This embodiment offers a platform technology which can provide quantitative information regarding a large number of different low-abundance proteins, peptides, and micro RNA under investigation using their specific binding receptor. Other components such as microfluidic channels, integrated microvalves or micropumps for flow control, sampling device with integrated cell lysis and filtration systems for sample preparation may be included. A lab-on-chip microfluidic system, including manipulating, capturing, lysing cell and lysate analysis, can be fabricated for a single cell analysis. Based on the platform technology we can target multiple specific applications (for example, a low-cost PSA screening system).
The embodiments of the present invention can help researchers to develop or detect biomarkers for different cancers. The techniques of the present invention can be used for large-scale proteomic analysis for the simultaneous measurement of thousands of proteins, for fast screening of proteins for new drug targets, and for routine screening of drugs to determine possible side effects. The system of the present invention can rapidly analyze the response of the targeted biomolecules and consequently accelerate the research and test on the animal models used in drug development. In addition, several research areas such as virus detection and single cell analysis in a microfluidic chip can benefit from the improved sensing technique of the present invention. Point of care (POC) systems based on Lab-on-a-chip devices have been developed in the recent decades and provide clinicians a low cost solution to access to a wealth of information of the cancer tissue. The technology of the present invention enables better screening of different type of cancers or diseases. Further, the cost of this POC system is relatively low, and thus attractive for large-scale use in screening and disease prevention in a variety of contexts.
This probe design of the invention can be used for thermo mechanical or thermo chemical patterning in contact or at a distance from the sample being patterned, in vacuum, air or other fluid. Similarly, this design can be used for static and dynamic thermomechanical analysis of localized regions of samples. In this application, the thermal element heats the tip 1003 when the probe is in contact with the sample. As the thermal element keeps increasing in temperature at a certain point it will melt the material under it. This will cause the cantilever to move; this movement can be detected and measured using a cantilever deflection detection mechanism. This mechanism can be the deflection element which is embedded on the cantilever 1005 or the laser optical lever of the AFM or SPM. This measurement allows the user to measure the melting point of a material.
Alternatively, an apparatus and a method for electromagnetic (EM) radiation detection (including radiation in the infrared/mid-IR/near-IR spectrum) can be facilitated by attaching a carbon nanotube (CNT) on a cantilever. The CNT contacts at least two separate electrically conductive traces formed by metal deposition or an implant process on the cantilever. A scanning stage, a light source, and instrumentation to synchronize and control the cantilevers may be used. The cantilever may also contain a bolometer in addition to the CNT. Joined bolometric and CNT detection may be used to calibrate the CNT's. In addition, blackbody radiation and ambient noise can be measured with the bolometer and cancelled out from the CNT measurement. Furthermore, a second CNT may be used as an emitter. CNT's can be used to emit light of certain frequency. This enables the use of a CNT emitter and a detector on the same cantilever. A Schottky contact is formed at the interface between the traces and the carbon nanotube. There are two Schottky contacts on each CNT. One of the two can be covered with a material that absorbs radiation of specific frequency. Since the contact area is submicron, the resolution is submicron and proportional to the contact area. In addition to single probes, the same structure can be made in the form of an array. EM radiation of certain wavelength is measured by measuring the change in resistance between the two traces, which corresponds to the absorption of certain wavelength by the CNT at the Schottky contact. These devices can be used as part of a scanning system to measure the specific IR spectra of a sample or simultaneous monitoring at various points of a sample, and correlate it to the horizontal movement of the cantilever on the sample. The device can also be mounted on a biopsy needle instead of a scanning stage, and used to monitor IR signals in vivo. Research has shown that cancerous cells have different IR signature compared to non-cancerous cells. An IR sensor mounted on a biopsy probe can act like the “eyes” inside the body and help the user to guide the probe to the location of the tumor.Materials
If is preferred that the cantilevers be highly compliant, then the cantilever's body may comprise of one of many types of materials or a combination of materials such as photoresist, SU-8, and polymers such as poly(dimethylsiloxane) (PDMS), polyimide, parylene, and elastomers such as silicone and rubber. Cantilevers made from these materials have low spring constants and therefore are highly compliant. Other materials include any material used to make cantilever structures that has been use in the past. Probes made of these materials are ideal for indentation measurements for example for cell elastography. They are also ideal for soft specimen scanning such as live cell.
Cantilevers made of polymer or elastomers or other soft materials are also ideal for high speed scanning. In scanning probe microscopy when in contact mode, scanning cantilevers that are very compliant tend to “stick” to the surface and move with the topographical changes, much akin to a “wet noodle” dragged along the surface with a minor on the top side. Laser response is ideal since it is very fast. This may allow even live cell imaging with great accuracy. Live cells tend to move so a high speed technique is very useful for this kind of imaging. In the embodiment of the present invention, as mentioned previously, a thermal or a displacement element is embedded in order to measure thermal or topographical changes or both. To achieve ultra high speeds in air and liquid, the user may need to first bring the probe in contact and then align the laser light and start scanning.
Metal or semimetal sensor may be made of antimony, gold, titanium, metals and semimetals including, but not limited to, Ag, Ni, Pt, Al, Cr, Pd, W, and metal alloys, such as Constantan, Karma, Isoelastic, Nichrome V, Pt—W, Pt—Cr, etc. Sensors may also be made of any type of thin film that exhibits MIT or MST at the temperatures of interest including vanadium dioxide (VO2).
The sensors described in the present invention may be combined with piezoelectric or other types of sensors and actuators. Piezoelectric materials include but are not limited to: berlinite (AlPO4), quartz, gallium orthophosphate, langasite, ceramics (such as PZT), sodium potassium niobate, polymers (such as polyvinylidene fluoride). For example, a piezoresistive sensor or a displacement sensor is combined with a piezoelectric actuator (active) on a cantilever. This cantilever can be used for atomic force microscopy applications or even material characterization applications.
Additional applications of these sensors include, a) Using the sensors as infrared spectrometers either on an AFM/SPM system or in some other arrangement, b) calorimetry, phase changes, and melting point measurement, c) modulating the temperature of a thermal probe to generate evanescent thermal waves in a material to thereby generate sub-surface images, d) static and dynamic thermomechanical analysis of localized regions of inhomogeneous samples, e) nano-heating using the thermal probe as a nanometer heater.
The features and advantages of the present invention described in the embodiments are presented for illustrative purposes only and should not be construed to limit the scope of the invention. Many modifications and variations of these embodiments are possible. To illustrate, one can shrink the dimensions of the sensors and cantilevers to submicron features or smaller to nano-cantilevers. One or two or all three dimensions may be in the submicron range. For instance, a cantilever or a two or four anchored suspended beam made of any of the materials mentioned having length 1 micron, width 200 nanometers, and thickness 100 nanometers, with the sensor having a 5 nanometers thickness.
The concepts described in the present invention can be used for cantilevers, diaphragms, clamped beams, wires, etc. These sensors can be used for scanning probe microscopes, atomic force microscopes, flow sensors, force and pressure sensors, inertial sensors, such as accelerometers and motion transducers, chemical and biological sensors. As described above, chemical and biological sensors may include one or more cantilevers coated with a material that exclusively attaches to a chemical or biological compound.
While the invention has been thus been described with reference to the embodiments, it will be readily understood by those skilled in the art that equivalents may be substituted for the various elements and modifications made without departing from the spirit and scope of the invention.
It is to be understood that all technical and scientific terms used in the present invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.REFERENCES
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1. An electrical resistor comprising:
- an insulating substrate;
- an electrical resistor deposited on said insulating substrate, said electrical resistor possesses the following properties: a) said electrical resistor is a metal or semimetal thin film, b) said electrical resistor has a temperature coefficient of resistance between (negative) −0.000001 per Kelvin and (positive) 0.000001 per Kelvin, c) said electrical resistor is at the crossover of the metal-insulator-transition regime, d) the plot of current (in the vertical axis) and voltage (in the horizontal axis) of said electrical resistor is linear, e) said electrical resistor has a thickness less than 20 nanometers.
2. An apparatus comprising:
- an insulating substrate;
- an electrical conductor deposited on said insulating substrate, said electrical conductor possesses the following properties: a) said electrical conductor is a metal or semimetal thin film, b) said electrical conductor has a temperature coefficient of resistance between (negative) −0.000001 per Kelvin and (positive) 0.000001 per Kelvin, c) said electrical conductor is at the crossover of the metal-insulator-transition regime, d) said electrical conductor has a thickness less than 20 nanometers.
3. The electrical resistor according to claim 1, wherein said electrical resistor is selected from the group consisting of: semimetals, antimony, metals, titanium, tungsten, metal oxides, and gold.
4. The electrical resistor according to claim 1, wherein said insulating substrate is selected from the group consisting of: silicon oxide, silicon nitride, polymer, parylene, polyimide, and SU-8.
3. The apparatus according to claim 2, wherein said electrical conductor is selected from the group consisting of: semimetals, antimony, metals, titanium, tungsten, metal oxides, and gold.
4. The apparatus according to claim 2, wherein said insulating substrate is selected from the group consisting of: silicon oxide, silicon nitride, polymer, parylene, polyimide, and SU-8.
5. An electrical resistor with the following characteristics:
- a) said electrical resistor is a metal or semimetal thin film;
- b) said electrical resistor has a temperature coefficient of resistance between (negative) −0.000001 per Kelvin and (positive) 0.000001 per Kelvin;
- c) said electrical resistor is at the crossover of the metal-insulator-transition regime;
- d) the plot of current (in the vertical axis) and voltage (in the horizontal axis) of said electrical resistor is linear;
- e) said electrical resistor has a thickness less than 20 nanometers.
6. The electrical resistor according to claim 5, wherein said electrical resistor is selected from the group consisting of: semimetals, antimony, metals, titanium, tungsten, metal oxides, and gold.
7. The apparatus according to claim 2, wherein said electrical conductor connects at least two circuit components selected from the group consisting of: transistors, diodes, capacitors, inductors, resistors, and power sources.
8. The apparatus according to claim 1, wherein said electrical resistor connects at least two circuit components selected from the group consisting of: transistors, diodes, capacitors, inductors, resistors, and power sources.
9. The electrical resistor according to claim 5, wherein said electrical resistor connects at least two circuit components selected from the group consisting of: transistors, diodes, capacitors, inductors, resistors, and power sources.
Filed: May 11, 2012
Publication Date: Sep 6, 2012
Inventor: Angelo Gaitas (Ann Arbor, MI)
Application Number: 13/469,724
International Classification: H01C 1/012 (20060101);