Increasing the speed of frequency-domain, homodyne thermoreflectance imaging.

Charge coupled device (CCD)-based thermoreflectance imaging using a "4-bucket" lock-in imaging algorithm is a well-established, powerful method for obtaining high spatial and thermal resolution two-dimensional thermal maps of optoelectronic, electronic, and micro-electro-mechanical systems devices. However, the technique is relatively slow, limiting broad commercial adoption. In this work, we examine the underlying limit on the image acquisition speed using the conventional "4-bucket" algorithm and show that the straightforward extension to an n-bucket technique by faster sampling does not address the underlying statistical bias in the data analysis and hence does not reduce the image acquisition time. Instead, we develop a modified "enhanced n-bucket" algorithm that halves the image acquisition time for every doubling of the number of buckets. We derive detailed statistical models of the algorithms and confirm both the models and the resulting speed enhancement experimentally, resulting in a practical means of significantly enhancing the speed and utility of CCD-based frequency domain, homodyne thermoreflectance imaging.

Spatially mapping charge carrier density and defects in organic electronics using modulation-amplified reflectance spectroscopy.

Charge-modulated optical spectroscopy is used to achieve dynamic two-dimensional mapping of the charge-carrier distribution in poly(3-hexylthiophene) thin-film transistors. The resulting in-channel distributions evolve from uniformly symmetric to asymmetrically saturated as the devices are increasingly biased. Furthermore, physical, chemical, and electrical defects are spatially resolved in cases where their presence is not obvious from the device performance.

Theoretical and experimental investigation of the thermal resolution and dynamic range of CCD-based thermoreflectance imaging.

We demonstrate thermal imaging using a charge-coupled device (CCD) thermoreflectance lock-in technique that achieves a record temperature resolution of 18 mK, 44 dB below the nominal dynamic range of the camera (from 72 to 116 dB) for 10(5) periods of measurement. We show that the quantization limit of the CCD camera does not set the lower bound on the precision of the technique. We present a theoretical description of the measurement technique, accounting for the effects of noise and nonideal analog-to-digital conversion, resulting in analytic expressions for the probability distribution function of the measured signals, and allowing for explicit calculation of resolution and error bars. The theory is tested against parametrically varied measurements and can be applied to other sampled lock-in measurements. We also experimentally demonstrate sub-quantization-limit imaging on a well-characterized model system, joule heating in a silicon resistor. The accuracy of the resistor thermoreflectance measurement is confirmed by comparing the results with those of a standard 3omega measurement.