Haifei Bao

A silicon integrated micro nano-positioning XY-stage for nano-manipulation

An integrated micro XY-stage with a 2 × 2 mm2 movable table is designed and fabricated for application in nanometer-scale operation and nanometric positioning precision. The device integrates the functions of both actuating and sensing in a monolithic chip and is mainly composed of a silicon-based XY-stage, comb-drive actuator and a displacement sensor, which are developed by using double-sided bulk-micromachining technology. The high-aspect-ratio comb-driven XY-stage is achieved by deep reactive ion etching (DRIE) on both sides of the wafer. The displacement sensor is formed on four vertical sidewall surface piezoresistors with a full Wheatstone bridge circuit, where a novel fabrication process of a vertical sidewall surface piezoresistor is proposed. Comprehensive design and analysis of the comb actuator, the piezoresistive displacement sensor and the XY-stage are given in full detail, and the experimental results verify the design and fabrication of the device. The final realization of the device shows that the sensitivity of the fabricated piezoresistive sensors is better than 1.17 mV µm−1 without amplification, and the linearity is better than 0.814%. Under 28.5 V driving voltage, a ±10 µm single-axis displacement is measured without crosstalk and the resonant frequency is measured at 983 Hz in air.

Single-wafer-processed nano-positioning XY-stages with trench-sidewall micromachining technology

For operation and manipulation with nanometric positioning precision, a single crystalline silicon micro XY-stage is developed by using double-sided bulk-micromachining technology. Front-side deep reactive ion etching combined with backside anisotropic etching constructs the high-aspect-ratio comb-driven XY-stage in a single standard silicon wafer (i.e., no silicon on insulator wafer is used). For integrating several electrostatic actuators in one silicon chip, different actuators are electrically isolated from each other using a trench-sidewall insulating technique. SiO2-refilled trench bars are formed on vertical trench sidewalls to isolate adjacent comb-drive elements. Combined with the reverse-biased p–n junction along the boron-diffused trench sidewall for comb driving, individual actuators can be operated independently. The developed XY-stage of 1600 × 1600 µm2 is suspended by four sets of folded-beam and bending-flexure composite springs. To maximize the moving distance, a two-segment comb finger with a gently curved transition is used for both improving the actuation efficiency and avoiding side instability of the stage. The experimental results verify the stage design including the gentle transition of a two-segment comb-drive scheme. Under 23 V driving voltage, a 10 µm moving stroke is measured in each of the four directions. Compared with a conventional comb structure, the two-segment comb fingers contribute 70% improvement in actuating amplitude. The positioning precision of the stage is evaluated with a nano-mechanical indenting experiment. A scanning probe microscopy probe with an electrical-heated nano tip is put in contact with the surface of a polymethyl methacrylate film that is coated on the stage surface. Along with the movement of the stage, pulsed heating on the nano tip produces serial nano-pitches. With the nano-indenting experiment, better than 18 nm positioning precision is obtained for the XY-stage.

AFM probes fabricated with masked-maskless combined anisotropic etching and p + surface doping

The paper presents a newly developed high-yield micro-fabrication technology for single-crystalline silicon atomic force microscope (AFM) probes. Both the tips and the cantilevers are simultaneously formed by a masked?maskless combined anisotropic etching process. Compared to a conventional tip-to-cantilever sequential fabrication scheme, this tip-and-cantilever simultaneous formation can effectively increase fabrication yield by avoiding the tips damaged during the following processed photolithographic steps for defining the cantilevers. By heavy boron doping at the surface, the conductive AFM probe provides an electrical path to the electric ground of the AFM that helps to eliminate the electrostatic accumulation of charges and, therefore, eliminate undesirable electrostatic forces between the probes and the samples. A fabrication yield as high as 90% has been obtained for the AFM probes for 4 inch wafers. The tips after oxidation-sharpening treatment generally have a radius of 10?30 nm. The cantilever spring constant can be well controlled in the range of 0.025?40 N m?1. High-quality sample scanning results with the formed AFM probes are obtained with a slightly better resolution than that from commercial probes without surface conductive treatment.

A heater-integrated scanning probe microscopy probe array with different tip radii for study of micro-nanosize effects on silicon-tip/polymer-film friction

Electric-heated cantilever-tip probes fabricated by micromachining techniques can be used for high-density data storage, nanopatterning, etc., where contact-scanning and thermal-plastic nanowritings are frequently implemented on the surface of a polymer thin-film such as polymethylmethacrylate (PMMA). In such kind of applications, micro-nanofriction effects, e.g., contacting-size and temperature effects of the tip/film friction system, will largely influence the performance of the applications. To elucidate the effects, present research fabricates a monolithically integrated probe array that comprises three scanning probe microscopy cantilever-tip probes with different tip radii of tens of nanometers, submicrometers and microns, respectively. The tip is enabled an electric-heating function by integrating a heating resistors on the tip. Using the tips, the tip/film friction experiment shows an obvious contacting-area effect. Within a wide temperature range, the friction signal and the normal force load exhibit a nonlinear relationship for the nanoradius tip but a linear relationship for the submicron tip. With the heated tips, the experiment directly reveals significant size effects on friction and adhesion behaviors. It is found that the glassy transition of the PMMA film can be characterized using the submicron tip, while the nanotip is suited to detect the secondary beta transition process. By fitting the experimental data into a power law with apparent friction coefficient included, the temperature-effect combined size effect of the micronano tip/polymer friction is modeled and discussed.

Micro cantilever probe array with integration of electro-thermal nano tip and piezoresistive sensor

A micro cantilever-lip silicon probe-array with integrated electro-thermal nano-lip and piezoresistive sensor has been presented for NEMS high-density data storage. Such a 1/spl times/10 probe-array is designed after the working principle studied. Both analysis and FEM simulation are used for modeling and designing with their results agreeing well, with a tolerance of only 5%. The devices are fabricated by using silicon bulk micromachining technology. The relationship between the resistance of the heater and the temperature of the tip is experimentally obtained and fitted with second order polynomial function. With the fitted results, the pulse-heating property of the devices is characterized. The tested results are in agreement with the simulation. Under pulsed 4V power supply and 3 /spl mu/s heating period, the tip can be heated to 463.15 K. Near 100 KHz writing rate can be realized, as 6.2 /spl mu/s is needed for cooling the heating resistor. The sensitivity of piezoresistivity is 5.4/spl times/10/sup -4/ under the contact force of 2/spl times/10/sup -7/ N, which is sufficient to reading the data pitch on PMMA media.

A novel monolithically integrated pressure, accelerometer and temperature composite sensor

The paper presents a novel single-side micromachined composite sensor, with a piezoresistive pressure sensor, a thermal-convection accelerometer and a thermometer monolithically integrated in one 2.5×2.5mm2 chip, for low-cost production and applications such as tire-pressure monitoring systems (TPMS). The accelerometer is based on heat convection, including a micro heater and two pairs of micro machined thermopile sensors for temperature difference sensing. The convective accelerometer sensitivities at the heater power of 10.90mW, 19.56mW and 30.12mW are 37.92µv/g, 85.04µv/g and 134.08µv/g, respectively. The pressure sensor sensitivity range 450KPa is about 0.038mV/V/KPa .The Non-linearity is less than ±1.06 % FS (Full Scale) and even in over load case of 700KPa Non-linearity is under ± 1. 62 % FS. In this boron ion implantation case, the temperature coefficient of polysilicon resistor is −578 ppm/°0.

Measurement Technology for Micro-Nanometer Devices

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Monolithic tri-axis cantilever high-shock accelerometers fabricated with a single-sided process in (111) wafers

Single-sided fabricated monolithic tri-axis piezoresistive high-shock accelerometers are reported in this paper. A single-cantilever structure and two dual-cantilever structures are designed and employed to detect the Z-axis and X-/Y-axis high-shock accelerations, respectively. Different longitudinal dimensions of the cantilevers can be achieved and well controlled with a (111) wafer single-sided process. The remained smooth backside facilitates simple post-packaging without chip bonding. The results of the high shock test show the sensitivity of X-/Y-axis and Z-axis is 0.80–0.85 μV/g and 1.36 μV/g, respectively. The proposed single-sided process is also promising to fabricate other complex structures with different longitudinal sizes.

Micro/NANO-Friction and Thermal-Mechanical Properties of Polymer Thin-Film Investigated with an Integrated SPM Probe Array

Size and temperature effects of micro/nano friction between a tiny tip and a polymer film are investigated. This topic is important in MEMS/NEMS such as high-density thermal-mechanical data storage on polymethylmethacrylate (PMMA) film. In present research, three electric-thermal probe-tips with varied apex dimensions are on-chip integrated to study the micro/nano friction and structural properties, which are remained as unsolved problems in MEMS/NEMS. Present experiments directly reveal significant size and temperature effects on micro/nano friction, adhesion and the structural transitions of PMMA thin film.

A Single-Wafer-Processed XY-Stage Fabricated with Trench-sidewall Doping and Refilled-Trench Isolating Technology

For nano-metric positioning and manipulation, a single-crystalline-silicon XY-stage is fabricated by using a double-sided bulk-micromachining technology. For defining different electrostatic actuators in one ordinary wafer (instead of SOI wafer), a trench-sidewall electric isolation method is developed. Previously insulator-refilled trench-bars are used to cut and isolate the different comb-drive actuating elements on the structural trench-sidewalls. Combined with the reverse-biasd isolation of p-n junctions along the boron-diffused trench- sidewall for comb-driving, individual actuators can be operated independently. For maximizing the actuating stroke that is limited by the fabricated minimal comb-gap, a two-segment comb with a gentle-curve transition is designed for both improving actuation-amplitude and avoiding side-instability of the stage. Under 23 V actuating voltage, the moving stroke is about 10 mum in each of the four directions. Compared with conventional comb structure, the new comb design contributes 70% improvement in driving amplitude. Nano pitches on PMMA film are recorded by an electric-heated SPM probe. Coated with PMMA film, the stage movement is precisely controlled, resulting in controllable nano recording.