Phase‐Change Reconfigurable Circuits Cheng‐Yuan Wen
Jeyanandh Paramesh Larry Pileggi Reconfigurable electronics are becoming a necessity to address increasing silicon costs and the need for flexible operation. Digital and analog circuits often use CMOS switches to achieve reconfiguration for programmable logic functions and for programmable gain or bandwidth. However, due to their high capacitive parasitics and high ON state resistance (RON), CMOS switches are not well‐suited to reconfiguring RF circuits in multi‐standard radios. Here, we propose a new approach for reconfiguration by implementing on‐chip switches using non‐
volatile phase‐change (PC) materials that feature high dynamic range ROFF and RON in the amorphous and crystalline states, with low parasitics. To prove the proposed concept, cross‐
coupled LC VCO’s with two different PC via‐reconfigurable inductors: (a) series connected and (b) coupling controlled have been designed and fabricated as demonstration vehicles, as shown in Fig. 1. The transistors, capacitors, resistors and inductor traces are fabricated in a 130 nm CMOS process, and flip‐chip integrated with a PC chip fabricated in an in‐house PC process (Fig. 2). The two LC VCOs can be band‐switched by PC‐switched reconfigurable inductors, coarsely tuned using a programmable capacitor array and finely tuned by MOS varactors. Measured results of the integrated VCOs show successful reconfiguration with wide frequency tuning. The characterized tuning ranges of the two designs are shown in Fig. 3 and Fig. 4, respectively. VDD
100 μm pad with solder bump
PC switch
VO+
8C
4C
2C
VDD
C
inductor in 0.13µm CMOS process
Cap SW8
Cap SW4
Cap SW2
Cap SW1
8C
GSG probe pads
4C
2C
VO+
series connection
(a)
VO‐
reflowed solder bumps
5 mm
GSG probe pads
C
PC switch w/ GSG pads
flip‐chip solder bumps
5 mm
PC switch
VDD
VS
VB
2.5 mm
Vcont
IBIAS
Bias switch network
VO+
2.5 mm
CMOS chip
VO‐
coupling controlled
Fig. 1: Reconfigurable PC switch VCO Integrated chip
PC chip
Fig. 2: Flip‐chip bonded VCO Frequency (GHz)
OFF state
ON state
7
(b)
12
8
Frequency (GHz)
to cross‐coupled NFETs
VO‐
6
5
4
3
OFF state
ON state
10
8
6
4
2
0
2
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Band index
Fig. 3: Frequency tuning of series connection VCO 30 | Center for Silicon System Implementation Research Summary
Band index
Fig. 4: Frequency tuning of coupling controlled VCO