Robert M. Young

Fabrication of micronozzles using low-temperature wafer-level bonding with SU-8

This paper describes a method for fabricating micronozzles using low-temperature wafer-level adhesive bonding with SU-8. The influence of different parameters on the bonding of structured wafers has been investigated. The surface energies of bonded wafers are measured to be in the range of 0.42–0.56 J m−2, which are comparable to those of some directly bonded wafers. Converging–diverging nozzle structures with throat widths as small as 3.6 µm are formed in an SU-8 film bonded with another SU-8 intermediate layer to produce sealed micronozzles. A novel interconnection technique is developed to interface and test the micronozzles with a macroscopic fluid delivery system to demonstrate the feasibility of the fabrication process. Leakage test results show that this low-temperature wafer bonding process is a viable MEMS fabrication technique for microfluidic applications.

A Four-Terminal, Inline, Chalcogenide Phase-Change RF Switch Using an Independent Resistive Heater for Thermal Actuation

An inline chalcogenide phase-change radio-frequency (RF) switch using germanium telluride and driven by an integrated, electrically isolated thin-film heater for thermal actuation has been fabricated. A voltage pulse applied to the heater terminals was used to transition the phase-change material between the crystalline and amorphous states. An ON-state resistance of 4.5 Ω (0.08 Ω-mm) with an OFF-state capacitance and resistance of 35 fF and 0.5 MΩ, respectively, were measured resulting in an RF switch cutoff frequency (Fco) of 1.0 THz and an OFF/ON resistance ratio of 105. The output third-order intercept point measured , with zero power consumption during steady-state operation, making it a nonvolatile RF switch. To the best of our knowledge, this is the first reported implementation of an RF phase change switch in a four-terminal, inline configuration.

Low-loss latching microwave switch using thermally pulsed non-volatile chalcogenide phase change materials

A high performance RF (radio-frequency) switch based on the phase change effect in germanium-telluride (GeTe) is described. Thermal pulses applied to a separate independent thin film heating element for 0.1–1.5 μs toggles the switch in a latching fashion. Being non-volatile, no power is required to hold the switch in the on- or off-state. State-of-the-art solid-state RF switches currently in use have an on-state loss of 1 dB; here, we demonstrate an inline phase change switch with a low on-state resistance showing over a frequency range of 0-40 GHz an insertion loss of just 0.1–0.24 dB.

12.5 THz Fco GeTe Inline Phase-Change Switch Technology for Reconfigurable RF and Switching Applications

Improvements to the GeTe inline phase-change switch (IPCS) technology have resulted in a record-performing radio-frequency (RF) switch. An ON-state resistance of 0.9 Ω (0.027 Ω·mm) with an OFF-state capacitance and resistance of 14.1 fF and 30 kΩ, respectively, were measured, resulting in a calculated switch cutoff frequency (Fco) of 12.5 THz. This represents the highest reported Fco achieved with chalcogenide switches to date. The threshold voltage (Vth) for these devices was measured at 3V and the measured third-order intercept point (TOI) was 72 dBm. Single-pole, single-throw (SPST) switches were fabricated, with a measured insertion loss less than 0.15 dB in the ON-state, and 15dB isolation in the OFF-state at 18 GHz. Single-pole, double-throw (SPDT) switches were fabricated using a complete backside process with through-substrate vias, with a measured insertion loss 0.25 dB, and 35dB isolation.

Development of cap-free sputtered GeTe films for inline phase change switch based RF circuits

Germanium telluride (GeTe) films have been recently demonstrated as the active element in low-loss RF switches where a 7.3 THz cut-off frequency (Fco) was achieved. In order to simultaneously realize the low ON-state transmission loss and large OFF-state isolation required for this application, significant optimization of the GeTe films was required. In particular, minimizing contact resistance (Rc) and sheet resistivity (Rsheet) without the use of a capping layer is a necessity. Varying the GeTe deposition conditions led to a wide range of structural, chemical, and electrical properties, which ultimately enabled the demonstration of a capless GeTe inline phase change switch (IPCS) structure. Conversely, improper deposition conditions led to extensive oxidation which would push Rc and Rsheet to unacceptable levels. In addition to its relevance for IPCS devices, this work has implications for the environmental stability of GeTe as a function of its physical morphology.

Thermal analysis of an indirectly heat pulsed non-volatile phase change material microwave switch

We show the finite element simulation of the melt/quench process in a phase change material (GeTe, germanium telluride) used for a radio frequency switch. The device is thermally activated by an independent NiCrSi (nickel chrome silicon) thin film heating element beneath a dielectric separating it electrically from the phase change layer. A comparison is made between the predicted and experimental minimum power to amorphize (MPA) for various thermal pulse powers and pulse time lengths. By including both the specific heat and latent heat of fusion for GeTe, we find that the MPA and the minimum power to crystallize follow the form of a hyperbola on the power time effect plot. We also find that the simulated time at which the entire center GeTe layer achieves melting accurately matches the MPA curve for pulse durations ranging from 75–1500 ns and pulse powers from 1.6–4 W.

Low-loss non-volatile phase-change RF switching technology for system reconfigurability and reliability

A novel phase-change microelectronics technology is described to enable wideband reconfigurable RF systems and components for EW, RADAR and communications applications. This technology can lower the development time and cost of DoD systems for new missions by enabling factory or mission re-programmability. It can also support component redundancy in system architectures with little impact to system performance.

Substrate agnostic monolithic integration of the inline phase-change switch technology

Omni-directional GeTe inline phase-change switches (IPCS) have been fabricated and heterogeneously integrated with commercial SiGe BiCMOS technology to create a reconfigurable receiver. The reconfigurable receiver required integrating thirteen (13) 8-port and two (2) 4-port omni-directional switch circuits with a commercial SiGe IC, requiring very stable and repeatable performance from the 112 integrated GeTe IPCS devices. Insertion loss, isolation, and cycling data will be presented, as well as performance issues encountered during the heterogeneous integration process. A new monolithic integration scheme is briefly discussed that is independent of the substrate and semiconductor technology used. This integration plan enables the monolithic fabrication of GeTe IPCS devices on any semiconductor technology, allowing low-loss, low-power, broadband reconfigurable RF systems and SoCs (system-on-chip) to be realized in any technology.

Examination of the temperature dependent electronic behavior of GeTe for switching applications

The DC and RF electronic behaviors of GeTe-based phase change material switches as a function of temperature, from 25 K to 375 K, have been examined. In its polycrystalline (ON) state, GeTe behaved as a degenerate p-type semiconductor, exhibiting metal-like temperature dependence in the DC regime. This was consistent with the polycrystalline (ON) state RF performance of the switch, which exhibited low resistance S-parameter characteristics. In its amorphous (OFF) state, the GeTe presented significantly greater DC resistance that varied considerably with bias and temperature. At low biases (<1 V) and temperatures (<200 K), the amorphous GeTe low-field resistance dramatically increased, resulting in exceptionally high amorphous-polycrystalline (OFF-ON) resistance ratios, exceeding 109 at cryogenic temperatures. At higher biases and temperatures, the amorphous GeTe exhibited nonlinear current-voltage characteristics that were best fit by a space-charge limited conduction model that incorporates the effect of a defect band. The observed conduction behavior suggests the presence of two regions of localized traps within the bandgap of the amorphous GeTe, located at approximately 0.26–0.27 eV and 0.56–0.57 eV from the valence band. Unlike the polycrystalline state, the high resistance DC behavior of amorphous GeTe does not translate to the RF switch performance; instead, a parasitic capacitance associated with the RF switch geometry dominates OFF state RF transmission.

Morphological analysis of GeTe in inline phase change switches

Crystallization and amorphization phenomena in indirectly heated phase change material-based devices were investigated. Scanning transmission electron microscopy was utilized to explore GeTe phase transition processes in the context of the unique inline phase change switch (IPCS) architecture. A monolithically integrated thin film heating element successfully converted GeTe to ON and OFF states. Device cycling prompted the formation of an active area which sustains the majority of structural changes during pulsing. A transition region on both sides of the active area consisting of polycrystalline GeTe and small nuclei (<15 nm) in an amorphous matrix was also observed. The switching mechanism, determined by variations in pulsing parameters, was shown to be predominantly growth-driven. A preliminary model for crystallization and amorphization in IPCS devices is presented.