ABSTRACT
Through via holes in fused silica are a key infrastructure element of microwave and millimeter-wave circuits and 3D integration. In this work, etching through via holes in ultra-thin fused silica wafers using deep reactive-ion etching (DRIE) and laser ablation was developed and analyzed. The experimental setup and process parameters for both methods are presented and compared. For DRIE, three types of mask materials including KMPR 1035 (Nippon Kayaku, Tokyo, Japan) photoresist, amorphous silicon and chromium-with their corresponding optimized processing recipes-were tested, aiming at etching through a 100 µm fused silica wafer. From the experiments, we concluded that using chromium as the masking material is the best choice when using DRIE. However, we found that the laser ablation method with a laser pulse fluence of 2.89 J/cm² and a pulse overlap of 91% has advantages over DRIE. The laser ablation method has a simpler process complexity, while offering a fair etching result. In particular, the sidewall profile angle is measured to be 75° to the bottom surface of the wafer, which is ideal for the subsequent metallization process. As a demonstration, a two-inch wafer with 624 via holes was processed using both technologies, and the laser ablation method showed better efficiency compared to DRIE.
ABSTRACT
PURPOSE: This article presents the study and simulation results of a millimeter (mm)-wave device for cancerous tissue detection. mm-Wave approach ensures cheaper equipment instead of the traditional terahertz (THz) frequency approach. A probe that could be implemented using inexpensive silicon technology is proposed, and it also permits integration of entire measuring tool for easy deployment. Skin cancer was chosen as it represents80% of all newly diagnosed cases and is the most common form of cancer in Australia. For an initial development and validation, due to data availability consideration in the open literature, basal cell carcinoma (BCC) was used for simulations. METHODS AND RESULTS: A probe, using high-frequency signals in the upper mm-wave frequency spectrum (90-300 GHz) to maximize the lateral resolution (mm precision) and allows the detection of tumors located at up to 0.5 mm deep in the skin, is proposed. A frequency-dependent relativity permittivity and an equivalent conductivity of skins were calculated based on the double Debye parameters. For the first time, electromagnetic (EM) models were generated and used along with a high-frequency EM simulator, ANSYS HFSS, to demonstrate the sensitivity of the concept. The following two scenarios were studied: in scenario one, a BCC layer of different thicknesses (10-3000 µm) was located on the top of the normal skin and, in scenario two, the BCC was embedded in normal skin at depths from 10 to 3000 µm. Variability using ±10% of the corresponding dielectric property was also considered. CONCLUSION: This study showed that the reflection coefficients vs frequency could capture useful information indicating the possible presence of BCC at mm-wave frequencies. Both magnitude and phase of the reflection coefficient were quantified, with two scenarios analyzed. It was found that a dual-band approach, 100-150 and 200-250 GHz, has the ability to highlight deviations from the normal skin.