Abstract: An apparatus and method are disclosed for characterizing semiconductor wafers or other test objects that can support acoustic waves. Source and receiving transducers are configured in various arrangements to respectively excite and detect acoustic waves (e.g., Lamb waves) in a wafer to be characterized. Signals representing the detected waves are digitally processed and used to compute a measurement set correlated with the waves' velocity in the wafer. A characterization sensitivity is provided that describes how different wafer characteristics of interest vary with changes in the propagation of the acoustic waves. Using the characterization sensitivity and measurement sets computed at a setup time when all wafer characteristics are known and one or more process times when at least one of the characteristics is not known the perturbation in wafer characteristics between the setup and the process times can be determined.

Abstract: There is provided an acoustic transducer which includes a membrane of selected size and shape supported at its edges spaced from a first conductive electrode by an integral support structure with the second conductive electrode comprising a thin metal film on the membrane. The active membrane area is undisturbed by etch vias.

Abstract: Acoustically thin capping structures and acoustic droplet ejectors having fluid wells and which use such capping structures to create fluid cells. The inventive capping structures permit the accurate positioning of the free surface of a fluid, permit acoustically induced fluid droplet ejection, and prevent fluid from spilling from the fluid wells. "Acoustically thin" means that the thickness of the capping structure is small enough that the acoustic energy that is lost passing through the capping structure is less than 50% of the incident acoustic energy.

Abstract: Techniques for obtaining an ejection rate independent, spatial relationship between an acoustic focal area and the free surface of a liquid. Variations in the spatial relationship are reduced or eliminated by applying substantially the same acoustic energy to the liquid's free surface during periods when droplets are not ejected as when they are, but at power levels insufficient to eject a droplet. During ejection periods in which a droplet is not ejected, the acoustic energy is applied at a lower level, but for a longer time. Because it is more convenient to measure and control, the transducer drive voltage is used to control the acoustic energy applied to the liquid's free surface.

Abstract: An electrostatic ultrasonic transducer formed on a semiconductor substrate by micro-machining wherein the transducer includes a silicon nitride membrane supported above the surface of the substrate by insulating supports; and the substrate and membrane define the electrodes of the transducer.

Abstract: An acoustic temperature and/or film thickness monitoring system for semiconductor wafers in which the velocity of acoustic waves in the wafer is employed to measure temperature and/or thickness.

Abstract: A liquid level control structure is provided comprising a plate having substantially flat top and bottom surfaces and an hourglass-shaped aperture containing a marking fluid. Protruding a known amount and at a known angle from opposite sides of the aperture waist are knife-edged lips that interact with the fluid's surface tension to control the location of an unbounded surface of the fluid.

Abstract: Techniques for improving droplet uniformity in acoustic ink printing. Row to row variations in an average droplet characteristic are reduced by controlling the electric power applied to the droplet ejectors of the individual rows. By applying the proper power to each row, the average droplet characteristic from the individual rows are made substantially. Another technique varies the efficiency of the individual droplet ejectors by physically trimming (such as with a laser) one or more of its components. Trimming may be performed on a droplet ejector's transducer, varactor, one or more associated resistors, or one or more capacitors. Yet another technique controls droplet ejector efficiency by electrically controlling the capacitance of a varactor associated with each droplet ejector, and thus each droplet ejector's efficiency.

Abstract: A printhead for an acoustic ink printer has a piezoelectric transducer on one surface of a substrate. A layer of a dielectric material is provided on the surface of the transducer away from the substrate. A Fresnel lens is formed in the surface of the dielectric layer away from the transducer, for focusing sound energy near the surface of a body of ink adjacent the dielectric layer. Thus the transducer and lens are both on the same side of the substrate. A pit may be formed in the substrate under the transducer. The transducer may be a body of piezoelectric material sandwiched between a pair of electrodes, the lower electrode of which has a thickness that is a quarter wave at the excitation frequency of the transducer.

Abstract: An acoustic microscope assembly for atomic level inspection of a target object includes a cantilever arm with a sharp tip on its lower surface and a zinc oxide piezoelectric thin film on its upper surface. High frequency excitation signals, having a frequency of at least 50 Megahertz, are applied to the piezoelectric thin film so as to generate high frequency acoustic signals that are transmitted through the sharp tip so as to impact on a target object. The assembly can either receive acoustic signals reflected by the target object, or it can receive acoustic signals that have propagated through the target object. One method of using this assembly is to apply a continuous wave signal to the piezoelectric thin film while scanning the target object, and measuring characteristics of the target object at various positions thereof by measuring the resonant frequency of the transmitted high frequency acoustic signals.

Abstract: A liquid level control structure and a method for its production. The controller is comprised of a plate having substantially flat top and bottom surfaces and an hourglass-shaped aperture containing a marking fluid. Protruding a known amount and at a known angle from opposite sides of the aperture waist are knife-edged lips that interact with the fluid's surface tension to control the location of an unbounded surface of the fluid.The method for producing the liquid level control structure uses semiconductor fabrication techniques. The aperture is formed in a semiconductor wafer using several etching steps, some of which act along the crystalline planes of the wafer. The lips are formed from etch stop layers deposited between etching steps, while the knife-edges are formed on the ends of the lips during an etching step. Beneficially, the location of the knife-edges relative to one surface of the wafer is independent of small variations in the thickness of the water.

Abstract: An acoustic ink printer transducer comprising a piezoelectric layer positioned between two suitable electrode materials. Also, a method for obtaining second harmonic operations from an acoustic ink printer transducer to enable ejection of a number of different ink droplet sizes from the acoustic ink printer thereby facilitating grey scale printing.

Abstract: This invention is an acoustic ink printer. It has a pool of ink (33) with a free surface (36). Underneath the ink is a print head (10) which has droplet ejectors (14) for irradiating the free surface (36) of the pool of ink (33) with focused acoustic radiation (44). Over the free surface (36) of the pool of ink (33) is a membrane (16), with one or more apertures (20) aligned with the droplet ejectors (14), in intimate contact with the free surface (36) of the pool of ink (33). The apertures 20 are substantially larger than the waist diameter (46) of the focused acoustic radiation (44). An external pressure source (50) maintains the meniscus (48) of the pool of ink (33) substantially in the focal plane (52) of the focused acoustic radiation (44) during operation of the droplet ejectors (14). A piezoelectric crystal (24) is in intimate contact with the pool of ink (33).

Abstract: The free ink surface levels of acoustic ink printers are controlled by cap structures that have substantially non-retroreflective aperture configurations. The non-retroreflective configurations of the apertures of these cap structures cause diffusive scattering or directional deflection of the reflected surface ripple waves, thereby significantly reducing the time that is required for the oscillatory perturbations, which are caused by reflection of the surface ripple waves that are generated during the droplet ejection process, to dissipate to a negligibly low amplitude in the critical local areas of the ejection sites. This, in turn, increases the droplet ejection rates at which printers having such cap structures can be operated asynchronously.

Abstract: An ejector for ejecting droplets from an ink-filled reservoir is disclosed. The ejector comprises a substrate with a generally planar surface. The substrate is submerged in the reservoir so that the substrate surface is parallel to the reservoir surface at a shallow predetermined depth. On the substrate surface around a center is a plurality of concentric, circular electrodes. A coupled oscillator excites the electrodes in a temporal relationship such that the capillary waves generated at the ink reservoir surface are reinforced so that droplets may be ejected from the reservoir at the center of the electrodes.

Abstract: An acoustic ink printhead with an integrated liquid level control layer is presented. A spacer layer is fixed to a substrate. Apertures are created in the spacer layer, which is then used as a mask, to define acoustic lenses and ink supply channels in the substrate. The apertures in the spacer layer used to define self-aligned acoustic lenses and to form the cavities to hold the ink reservoirs for each ejector. The thickness of the spacer layer is set so that acoustic waves from the acoustic lens below are focused at the free surface of the ink which maintains its level at the top of the spacer layer by capillary action.

Abstract: A method of fabricating an acoustic ink printhead with an integrated liquid level control layer is presented. With standard photolithographic techniques, acoustic lenses and ink supply channels are defined in a substrate. Apertures are created in a spacer layer plate to define cavities to hold the ink reservoirs for each ejector. Corresponding alignment holes also made in the substrate and in the spacer layer plate. With spheres matching the size of the alignment holes, the spheres engage the alignment holes to precisely align the apertures in the spacer layer plate with the acoustic lenses in the substrate. The plate and substrate are then bonded for an integrated acoustic printhead with liquid level control by capillary action.

Abstract: An acoustic microscope in which acoustic energy is focused onto a membrane which includes an aperture which is a fraction of the size of the focal spot of the acoustic beam at the membrane to form fringing fields on the other side of the membrane. Acoustic energy reflected from the membrane is detected. An object to be examined is placed in cooperative relationship with the fringing fields.

Abstract: In accordance with the present invention, an acoustic ink printer comprises a pool of liquid ink having a free surface in intimate contact with the inner face of a perforated membrane. The printer addresses all pixel positions within its image field via substantially uniform, relatively large diameter apertures which extend through the membrane on centers that are aligned with respective ones of the pixel positions. In operation, one or more focused acoustic beams selectively eject individual droplets of ink from the ink menisci that extend across the apertures. Accordingly, the membrane is positioned and the bias pressure that is applied to the ink is selected so that the menisci essentially remain within the focal plane of such beam or beams.

Abstract: An acoustic microscope surface inspection system and method in which pulses of high frequency electrical energy are applied to a transducer which forms and focuses acoustic energy onto a selected location on the surface of an object and receives energy from the location and generates electrical pulses. The phase of the high frequency electrical signal pulses are stepped with respected to the phase of a reference signal at said location. An output signal is generated which is indicative of the surface of said selected location. The object is scanned to provide output signals representative of the surface at a plurality of surface locations.