IMEC is inviting partners to join a programme to develop new types of embedded RAM (eRAM) for future applications where large amounts on on-chip memory are expected to be needed at the 45nm node.

The eRAM is not envisaged as replacing traditional SRAM for first-level cache memory, nor embedded flash or ROM, rather it is seen as a dense, space-saving, volatile memory which is suitable for major applications in the future where memory will take between 80 per cent and 90 per cent of a chip’s surface area.

Embedded DRAM has never been widely accepted as a mainstream technology option because of limited availability, process complexity and cost issues.

IMEC has three approaches to eRAM. One is direct tunnelling RAM where a flash structure, using oxides around 1.5nm thick, are used to store a charge on either a floating gate or a charge-trapping layer. High-k materials are being considered to lower the write/erase voltages, and a 10ns programming time at 45nm is considered feasible.

The second approach is using the ferroelectric field effect transistor (FeFET) which has better scalability than capacitor-based ferroelectric RAM. High-k materials can have a big effect on FeFET when used as a buffer layer between the channel and the ferroelectric in order to lower the write/erase voltages.

The third approach is based on the floating body cell, a concept based on the memory effect in silicon-on-insulator (SOI) devices. The technology is being adapted for planar as well as FinFET device structures. Preliminary retention results, obtained on partially depleted SOI MOSFETs programmed by impact ionisation, show the memory effect in scaled-down SOI technology.

IMEC reckons that its long experience in these technologies will mean that results can be generated in a timeframe of six to eighteen months.

Biochip research

Meanwhile, IMEC has developed a prototype 1cm³ 3D stacked system-in-cube (SiC) for wireless bioelectronic communications systems.

The cube contains a radio and digital signal processing (DSP) which can be used widely for wireless products like gathering medical information or environmental data such as temperature, pressure, and humidity can be transmitted when the appropriate sensor is applied.

It will first be used in a wearable, wireless electroencephalogram (EEG) for measuring activity in the brain.

Using the cube, patients can wear a comfortable device and maintain maximum mobility during the electroencephalogram, eliminating the hospital stay traditionally required for this procedure. 

The system-in-cube (SiC) was developed as part of IMEC's Human++ programme, which envisions similar SiCs as sensor nodes constituting a body area network.

The cube integrates a commercial low-power 8Mips microcontroller and a 2.4GHz wireless transceiver, crystals and other necessary passives, as well as a custom-designed matched dipole antenna.

Integration was achieved by 3D stacking of separate layers with different functionality. Each layer connects to its neighbouring layers through a dual row of fine pitch solder balls. This generic stacking technique allows any kind of module build-up; each layer can have dedicated functionality such as computing, wireless communication, sensing, power scavenging and so on. The bottom layer has a BGA (ball grid array) footprint, allowing standard techniques for module mounting.

Applications range from standalone sensor units to wireless multi-hop beacons. The tasks of the microcontroller unit range from adjusting sensor preamps and digitization to data interpretation, forward error coding and MAC (medium access control) implementations from low to medium complexity. The 12-bit microcontroller ADC provides enough dynamic range for most sensors to be directly interfaced with the module.

The stacking feature allows integrating a specific sensor into a single layer, resulting in an application-specific cubic sensor module.

Future developments will focus on size and power reduction. Adding an extra stack layer with solar cells and energy-storage circuitry will offer a complete standalone solution.